fix(consensus): propose locked block when it is available

internal/consensus/state_proposaler.go

@@ -86,12 +86,22 @@ func (p *Proposaler) Set(proposal *types.Proposal, receivedAt time.Time, rs *cst
 }
 
 // Create creates, sings and sends a created proposal to the queue
+//
+// We prioritize LockedBlock. If it's not set, then we use ValidBlock.
 // To create a proposal is used RoundState.ValidBlock if it isn't nil and valid, otherwise create a new one
 func (p *Proposaler) Create(ctx context.Context, height int64, round int32, rs *cstypes.RoundState) error {
-	// If there is valid block, choose that.
-	block, blockParts := rs.ValidBlock, rs.ValidBlockParts
-	// Create on block
-	if !p.checkValidBlock(rs) {
+	create := false
+	// If we are locked on some block, propose that.
+	// We don't check the timestamp in this case, as the block is already valid
+	block, blockParts := rs.LockedBlock, rs.LockedBlockParts
+	// when no locked block, use valid block
+	if block == nil || blockParts == nil {
+		block, blockParts = rs.ValidBlock, rs.ValidBlockParts
+		create = !p.checkValidBlock(rs)
+	}
+
+	// Create a block
+	if create {
 		var err error
 		start := time.Now()
 		block, blockParts, err = p.createProposalBlock(ctx, round, rs)