diff --git a/src/main/java/uk/gov/hmcts/darts/arm/model/batch/ArmBatchItems.java b/src/main/java/uk/gov/hmcts/darts/arm/model/batch/ArmBatchItems.java
index 4abbacbea8..8535964fa8 100644
--- a/src/main/java/uk/gov/hmcts/darts/arm/model/batch/ArmBatchItems.java
+++ b/src/main/java/uk/gov/hmcts/darts/arm/model/batch/ArmBatchItems.java
@@ -4,12 +4,13 @@
 import uk.gov.hmcts.darts.arm.model.ArchiveRecord;
 
 import java.util.ArrayList;
+import java.util.Collections;
 import java.util.List;
 
 
 public class ArmBatchItems {
     @Getter
-    private final List<ArmBatchItem> items = new ArrayList<>();
+    private final List<ArmBatchItem> items = Collections.synchronizedList(new ArrayList<>());
 
     public void add(ArmBatchItem batchItem) {
         items.add(batchItem);
diff --git a/src/main/resources/application.yaml b/src/main/resources/application.yaml
index a4a05edaab..7d8e45b1e8 100644
--- a/src/main/resources/application.yaml
+++ b/src/main/resources/application.yaml
@@ -512,7 +512,7 @@ darts:
           at-most-for: PT45M
       unstructured-to-arm-batch-processor:
         max-arm-manifest-items: 100
-        threads: 30
+        threads: 10
         async-timeout: 90m
       dets-to-arm-batch-processor:
         max-arm-manifest-items: 100