diff --git a/compiler/src/dotty/tools/dotc/core/TypeComparer.scala b/compiler/src/dotty/tools/dotc/core/TypeComparer.scala
index 47f36255de81..c00afa3f06d2 100644
--- a/compiler/src/dotty/tools/dotc/core/TypeComparer.scala
+++ b/compiler/src/dotty/tools/dotc/core/TypeComparer.scala
@@ -2586,6 +2586,11 @@ class TypeComparer(@constructorOnly initctx: Context) extends ConstraintHandling
         provablyDisjoint(tp1, gadtBounds(tp2.symbol).hi) || provablyDisjoint(tp1, tp2.superType)
       case (tp1: TermRef, tp2: TermRef) if isEnumValueOrModule(tp1) && isEnumValueOrModule(tp2) =>
         tp1.termSymbol != tp2.termSymbol
+      case (tp1: TermRef, tp2: TypeRef) if isEnumValueOrModule(tp1) && !tp1.classSymbols.exists(_.derivesFrom(tp2.classSymbol)) =>
+        // Note: enum values may have multiple parents
+        true
+      case (tp1: TypeRef, tp2: TermRef) if isEnumValueOrModule(tp2) && !tp2.classSymbols.exists(_.derivesFrom(tp1.classSymbol)) =>
+        true
       case (tp1: Type, tp2: Type) if defn.isTupleType(tp1) =>
         provablyDisjoint(tp1.toNestedPairs, tp2)
       case (tp1: Type, tp2: Type) if defn.isTupleType(tp2) =>
diff --git a/compiler/src/dotty/tools/dotc/core/TypeOps.scala b/compiler/src/dotty/tools/dotc/core/TypeOps.scala
index a842c5e58261..86c8446750c0 100644
--- a/compiler/src/dotty/tools/dotc/core/TypeOps.scala
+++ b/compiler/src/dotty/tools/dotc/core/TypeOps.scala
@@ -692,15 +692,24 @@ object TypeOps:
    */
   private def instantiateToSubType(tp1: NamedType, tp2: Type)(using Context): Type = {
     // In order for a child type S to qualify as a valid subtype of the parent
-    // T, we need to test whether it is possible S <: T. Therefore, we replace
-    // type parameters in T with tvars, and see if the subtyping is true.
-    val approximateTypeParams = new TypeMap {
+    // T, we need to test whether it is possible S <: T.
+    //
+    // The check is different from subtype checking due to type parameters and
+    // `this`. We perform the following operations to approximate the parameters:
+    //
+    // 1. Replace type parameters in T with tvars
+    // 2. Replace `A.this.C` with `A#C` (see tests/patmat/i12681.scala)
+    //
+    val approximateParent = new TypeMap {
       val boundTypeParams = util.HashMap[TypeRef, TypeVar]()
 
       def apply(tp: Type): Type = tp.dealias match {
         case _: MatchType =>
           tp // break cycles
 
+        case ThisType(tref: TypeRef) if !tref.symbol.isStaticOwner =>
+          tref
+
         case tp: TypeRef if !tp.symbol.isClass =>
           def lo = LazyRef.of(apply(tp.underlying.loBound))
           def hi = LazyRef.of(apply(tp.underlying.hiBound))
@@ -787,7 +796,7 @@ object TypeOps:
     // we manually patch subtyping check instead of changing TypeComparer.
     // See tests/patmat/i3645b.scala
     def parentQualify(tp1: Type, tp2: Type) = tp1.classSymbol.info.parents.exists { parent =>
-      parent.argInfos.nonEmpty && approximateTypeParams(parent) <:< tp2
+      parent.argInfos.nonEmpty && approximateParent(parent) <:< tp2
     }
 
     def instantiate(): Type = {
@@ -797,8 +806,8 @@ object TypeOps:
 
     if (protoTp1 <:< tp2) instantiate()
     else {
-      val protoTp2 = approximateTypeParams(tp2)
-      if (protoTp1 <:< protoTp2 || parentQualify(protoTp1, protoTp2)) instantiate()
+      val approxTp2 = approximateParent(tp2)
+      if (protoTp1 <:< approxTp2 || parentQualify(protoTp1, approxTp2)) instantiate()
       else NoType
     }
   }
diff --git a/compiler/src/dotty/tools/dotc/transform/SymUtils.scala b/compiler/src/dotty/tools/dotc/transform/SymUtils.scala
index eae6241ed6e8..f8b276d52088 100644
--- a/compiler/src/dotty/tools/dotc/transform/SymUtils.scala
+++ b/compiler/src/dotty/tools/dotc/transform/SymUtils.scala
@@ -100,6 +100,8 @@ object SymUtils:
     def whyNotGenericSum(declScope: Symbol)(using Context): String =
       if (!self.is(Sealed))
         s"it is not a sealed ${self.kindString}"
+      else if (!self.isOneOf(AbstractOrTrait))
+        s"it is not an abstract class"
       else {
         val children = self.children
         val companionMirror = self.useCompanionAsMirror
diff --git a/compiler/src/dotty/tools/dotc/transform/patmat/Space.scala b/compiler/src/dotty/tools/dotc/transform/patmat/Space.scala
index 7a0ef358fc40..569497b3d50d 100644
--- a/compiler/src/dotty/tools/dotc/transform/patmat/Space.scala
+++ b/compiler/src/dotty/tools/dotc/transform/patmat/Space.scala
@@ -105,7 +105,7 @@ trait SpaceLogic {
   def signature(unapp: TermRef, scrutineeTp: Type, argLen: Int): List[Type]
 
   /** Get components of decomposable types */
-  def decompose(tp: Type): List[Space]
+  def decompose(tp: Type): List[Typ]
 
   /** Whether the extractor covers the given type */
   def covers(unapp: TermRef, scrutineeTp: Type): Boolean
@@ -176,6 +176,8 @@ trait SpaceLogic {
         ss.forall(isSubspace(_, b))
       case (Typ(tp1, _), Typ(tp2, _)) =>
         isSubType(tp1, tp2)
+        || canDecompose(tp1) && tryDecompose1(tp1)
+        || canDecompose(tp2) && tryDecompose2(tp2)
       case (Typ(tp1, _), Or(ss)) =>  // optimization: don't go to subtraction too early
         ss.exists(isSubspace(a, _)) || tryDecompose1(tp1)
       case (_, Or(_)) =>
@@ -337,9 +339,7 @@ class SpaceEngine(using Context) extends SpaceLogic {
       val res = TypeComparer.provablyDisjoint(tp1, tp2)
 
       if (res) Empty
-      else if (tp1.isSingleton) Typ(tp1, true)
-      else if (tp2.isSingleton) Typ(tp2, true)
-      else Typ(AndType(tp1, tp2), true)
+      else Typ(AndType(tp1, tp2), decomposed = true)
     }
   }
 
@@ -591,14 +591,27 @@ class SpaceEngine(using Context) extends SpaceLogic {
     }
 
   /** Decompose a type into subspaces -- assume the type can be decomposed */
-  def decompose(tp: Type): List[Space] =
+  def decompose(tp: Type): List[Typ] =
     tp.dealias match {
       case AndType(tp1, tp2) =>
-        intersect(Typ(tp1, false), Typ(tp2, false)) match {
-          case Or(spaces) => spaces.toList
-          case Empty => Nil
-          case space => List(space)
-        }
+        def decomposeComponent(tpA: Type, tpB: Type): List[Typ] =
+          decompose(tpA).flatMap {
+            case Typ(tp, _) =>
+              if tp <:< tpB then
+                Typ(tp, decomposed = true) :: Nil
+              else if tpB <:< tp then
+                Typ(tpB, decomposed = true) :: Nil
+              else if TypeComparer.provablyDisjoint(tp, tpB) then
+                Nil
+              else
+                Typ(AndType(tp, tpB), decomposed = true) :: Nil
+          }
+
+        if canDecompose(tp1) then
+          decomposeComponent(tp1, tp2)
+        else
+          decomposeComponent(tp2, tp1)
+
       case OrType(tp1, tp2) => List(Typ(tp1, true), Typ(tp2, true))
       case tp if tp.isRef(defn.BooleanClass) =>
         List(
@@ -833,6 +846,9 @@ class SpaceEngine(using Context) extends SpaceLogic {
 
     if (!exhaustivityCheckable(sel)) return
 
+    debug.println("checking " + _match.show)
+    debug.println("selTyp = " + selTyp.show)
+
     val patternSpace = Or(cases.foldLeft(List.empty[Space]) { (acc, x) =>
       val space = if (x.guard.isEmpty) project(x.pat) else Empty
       debug.println(s"${x.pat.show} ====> ${show(space)}")
diff --git a/scaladoc/src/dotty/tools/scaladoc/tasty/TypesSupport.scala b/scaladoc/src/dotty/tools/scaladoc/tasty/TypesSupport.scala
index ca61a47ef5b7..5eda3ad7f5bc 100644
--- a/scaladoc/src/dotty/tools/scaladoc/tasty/TypesSupport.scala
+++ b/scaladoc/src/dotty/tools/scaladoc/tasty/TypesSupport.scala
@@ -27,14 +27,8 @@ trait TypesSupport:
       case ThisType(tpe) => inner(tpe)
       case AnnotatedType(tpe, _) => inner(tpe)
       case AppliedType(tpe, _) => inner(tpe)
-      case tp @ TermRef(qual, typeName) =>
-        qual match
-        case _: TypeRepr | _: NoPrefix => Some(tp.termSymbol)
-        case other => None
-      case tp @ TypeRef(qual, typeName) =>
-        qual match
-        case _: TypeRepr | _: NoPrefix => Some(tp.typeSymbol)
-        case other => None
+      case tp @ TermRef(qual, typeName) => Some(tp.termSymbol)
+      case tp @ TypeRef(qual, typeName) => Some(tp.typeSymbol)
 
     val typeSymbol = extractTypeSymbol(method.returnTpt)
 
@@ -204,8 +198,7 @@ trait TypesSupport:
       case tp @ TypeRef(qual, typeName) =>
         qual match {
           case r: RecursiveThis => texts(s"this.$typeName")
-          case _: TypeRepr | _: NoPrefix => link(tp.typeSymbol)
-          case other => noSupported(s"TypeRepr: $tp")
+          case _: TypeRepr => link(tp.typeSymbol)
         }
         // convertTypeOrBoundsToReference(reflect)(qual) match {
         //     case TypeReference(label, link, xs, _) => TypeReference(typeName, link + "/" + label, xs, true)
diff --git a/tests/patmat/i10667.scala b/tests/patmat/i10667.scala
new file mode 100644
index 000000000000..fde5021929fc
--- /dev/null
+++ b/tests/patmat/i10667.scala
@@ -0,0 +1,15 @@
+sealed trait A
+
+enum Nums {
+  case One
+  case Two extends Nums with A
+  case Three
+}
+
+object Test {
+  val list = List[Nums & A](Nums.Two)
+
+  list.map {
+    case Nums.Two => ()
+  }
+}
diff --git a/tests/patmat/i12475.scala b/tests/patmat/i12475.scala
new file mode 100644
index 000000000000..11ff389df318
--- /dev/null
+++ b/tests/patmat/i12475.scala
@@ -0,0 +1,20 @@
+sealed trait Ty {
+  type T
+}
+
+class TUnit() extends Ty {
+  type T = Unit
+}
+
+case object TUnit extends TUnit()
+
+final case class TFun(dom: Ty, cod: Ty) extends Ty {
+  type T = dom.T => cod.T
+}
+
+def default(ty: Ty): ty.T = (ty: ty.type & Ty) match {
+  case a: (ty.type & TUnit) => (): a.T
+  case a: (ty.type & TFun) =>
+    val f = { (x: a.dom.T) => default(a.cod) }
+    f: a.T
+}
diff --git a/tests/patmat/i12475b.scala b/tests/patmat/i12475b.scala
new file mode 100644
index 000000000000..799d95c0477b
--- /dev/null
+++ b/tests/patmat/i12475b.scala
@@ -0,0 +1,14 @@
+trait SomeRestriction
+
+enum ADT {
+  case A
+  case B extends ADT with SomeRestriction
+}
+
+object MinimalExample {
+  val b: ADT & SomeRestriction = ADT.B
+
+  b match {
+    case ADT.B => ???
+  }
+}
diff --git a/tests/patmat/i12546.scala b/tests/patmat/i12546.scala
new file mode 100644
index 000000000000..23cbfaa77c06
--- /dev/null
+++ b/tests/patmat/i12546.scala
@@ -0,0 +1,14 @@
+trait SomeRestriction
+
+enum ADT {
+  case A extends ADT
+  case B extends ADT with SomeRestriction
+}
+
+object MinimalExample {
+  val b: ADT & SomeRestriction = ADT.B
+
+  b match {
+    case ADT.B => ???
+  }
+}
diff --git a/tests/patmat/i12559.check b/tests/patmat/i12559.check
new file mode 100644
index 000000000000..34be8d4104f9
--- /dev/null
+++ b/tests/patmat/i12559.check
@@ -0,0 +1,2 @@
+10: Match case Unreachable
+27: Match case Unreachable
diff --git a/tests/patmat/i12559.scala b/tests/patmat/i12559.scala
new file mode 100644
index 000000000000..1f043d21e5bd
--- /dev/null
+++ b/tests/patmat/i12559.scala
@@ -0,0 +1,35 @@
+package akka.event
+
+object TestA:
+  sealed trait LogEvent
+
+  object LogEvent:
+    def myOrdinal(e: LogEvent): Int = e match
+      case e: Error => 0
+      // case e: Warning => 1
+      case e: LogEventWithMarker => 2
+
+
+  class Error() extends LogEvent
+  class Error2() extends Error() with LogEventWithMarker
+
+  // case class Warning() extends LogEvent
+
+  sealed trait LogEventWithMarker extends LogEvent
+
+object TestB:
+  sealed trait LogEvent
+
+  object LogEvent:
+    def myOrdinal(e: LogEvent): Int = e match
+      case e: Error => 0
+      case e: Warning => 1
+      case e: LogEventWithMarker => 2
+
+
+  case class Error() extends LogEvent
+  class Error2() extends Error() with LogEventWithMarker
+
+  case class Warning() extends LogEvent
+
+  sealed trait LogEventWithMarker extends LogEvent
\ No newline at end of file
diff --git a/tests/patmat/i12602.scala b/tests/patmat/i12602.scala
new file mode 100644
index 000000000000..3dac513a930c
--- /dev/null
+++ b/tests/patmat/i12602.scala
@@ -0,0 +1,2 @@
+sealed class Foo[T]
+object Foo extends Foo[Nothing]
diff --git a/tests/patmat/i12681.scala b/tests/patmat/i12681.scala
new file mode 100644
index 000000000000..b367e1563611
--- /dev/null
+++ b/tests/patmat/i12681.scala
@@ -0,0 +1,20 @@
+object Examples {
+
+  case class Leaf1() extends i.Root
+  case class Leaf2() extends i.Branch
+
+  val i = new Inner()
+
+  class Inner {
+
+    sealed trait Root
+    sealed trait Branch extends Root
+
+    // simulate ordinal method of a Mirror.SumOf generated at this call site
+    def myOrdinal(r: Root): Int = r match {
+      case _: Examples.Leaf1  => 0
+      case _: Inner.this.Branch => 1
+    }
+  }
+
+}
\ No newline at end of file