diff --git a/ReactCommon/fabric/mounting/Differentiator.cpp b/ReactCommon/fabric/mounting/Differentiator.cpp
index 9f9f60207dc..6661d542440 100644
--- a/ReactCommon/fabric/mounting/Differentiator.cpp
+++ b/ReactCommon/fabric/mounting/Differentiator.cpp
@@ -54,7 +54,13 @@ class TinyMap final {
     // then we don't need to clean.
     cleanVector(erasedAtFront_ != numErased_);
 
-    return begin_();
+    Iterator it = begin_();
+
+    if (it != nullptr) {
+      return it + erasedAtFront_;
+    }
+
+    return nullptr;
   }
 
   inline Iterator end() {
@@ -71,6 +77,10 @@ class TinyMap final {
 
     assert(key != 0);
 
+    if (begin_() == nullptr) {
+      return end();
+    }
+
     for (auto it = begin_() + erasedAtFront_; it != end(); it++) {
       if (it->first == key) {
         return it;
@@ -86,14 +96,14 @@ class TinyMap final {
   }
 
   inline void erase(Iterator iterator) {
-    numErased_++;
-
     // Invalidate tag.
     iterator->first = 0;
 
     if (iterator == begin_() + erasedAtFront_) {
       erasedAtFront_++;
     }
+
+    numErased_++;
   }
 
  private:
@@ -643,7 +653,7 @@ static void calculateShadowViewMutationsOptimizedMoves(
       }
 
       // At this point, oldTag is -1 or is in the new list, and hasn't been
-      // inserted or matched yet We're not sure yet if the new node is in the
+      // inserted or matched yet. We're not sure yet if the new node is in the
       // old list - generate an insert instruction for the new node.
       auto const &newChildPair = newChildPairs[newIndex];
       insertMutations.push_back(ShadowViewMutation::InsertMutation(
@@ -656,7 +666,9 @@ static void calculateShadowViewMutationsOptimizedMoves(
     for (auto it = newInsertedPairs.begin(); it != newInsertedPairs.end();
          it++) {
       // Erased elements of a TinyMap will have a Tag/key of 0 - skip those
-      // These *should* be removed by the map, but are not always.
+      // These *should* be removed by the map; there are currently no KNOWN
+      // cases where TinyMap will do the wrong thing, but there are not yet
+      // any unit tests explicitly for TinyMap, so this is safer for now.
       if (it->first == 0) {
         continue;
       }
diff --git a/ReactCommon/fabric/mounting/tests/MountingTest.cpp b/ReactCommon/fabric/mounting/tests/MountingTest.cpp
index 4783516bf1c..52361e23dc5 100644
--- a/ReactCommon/fabric/mounting/tests/MountingTest.cpp
+++ b/ReactCommon/fabric/mounting/tests/MountingTest.cpp
@@ -77,6 +77,11 @@ TEST(MountingTest, testMinimalInstructionGeneration) {
   auto childD = makeNode(viewComponentDescriptor, 103, {});
   auto childE = makeNode(viewComponentDescriptor, 104, {});
   auto childF = makeNode(viewComponentDescriptor, 105, {});
+  auto childG = makeNode(viewComponentDescriptor, 106, {});
+  auto childH = makeNode(viewComponentDescriptor, 107, {});
+  auto childI = makeNode(viewComponentDescriptor, 108, {});
+  auto childJ = makeNode(viewComponentDescriptor, 109, {});
+  auto childK = makeNode(viewComponentDescriptor, 110, {});
 
   auto family = viewComponentDescriptor.createFamily(
       {10, SurfaceId(1), nullptr}, nullptr);
@@ -107,6 +112,17 @@ TEST(MountingTest, testMinimalInstructionGeneration) {
       generateDefaultProps(viewComponentDescriptor),
       std::make_shared<SharedShadowNodeList>(SharedShadowNodeList{
           childB, childA, childD, childF, childE, childC})});
+  auto shadowNodeV7 = shadowNodeV6->clone(ShadowNodeFragment{
+      generateDefaultProps(viewComponentDescriptor),
+      std::make_shared<SharedShadowNodeList>(SharedShadowNodeList{childF,
+                                                                  childE,
+                                                                  childC,
+                                                                  childD,
+                                                                  childG,
+                                                                  childH,
+                                                                  childI,
+                                                                  childJ,
+                                                                  childK})});
 
   // Injecting a tree into the root node.
   auto rootNodeV1 = std::static_pointer_cast<RootShadowNode const>(
@@ -139,6 +155,11 @@ TEST(MountingTest, testMinimalInstructionGeneration) {
           ShadowNodeFragment{ShadowNodeFragment::propsPlaceholder(),
                              std::make_shared<SharedShadowNodeList>(
                                  SharedShadowNodeList{shadowNodeV6})}));
+  auto rootNodeV7 = std::static_pointer_cast<RootShadowNode const>(
+      rootNodeV6->ShadowNode::clone(
+          ShadowNodeFragment{ShadowNodeFragment::propsPlaceholder(),
+                             std::make_shared<SharedShadowNodeList>(
+                                 SharedShadowNodeList{shadowNodeV7})}));
 
   // Layout and diff
   std::vector<LayoutableShadowNode const *> affectedLayoutableNodesV1{};
@@ -307,6 +328,23 @@ TEST(MountingTest, testMinimalInstructionGeneration) {
   assert(mutations5[3].type == ShadowViewMutation::Insert);
   assert(mutations5[3].newChildShadowView.tag == 105);
   assert(mutations5[3].index == 3);
+
+  auto mutations6 = calculateShadowViewMutations(
+      DifferentiatorMode::OptimizedMoves, *rootNodeV6, *rootNodeV7);
+
+  // The order and exact mutation instructions here may change at any time.
+  // This test just ensures that any changes are intentional.
+  // This test, in particular, ensures that a bug has been fixed: that with
+  // a particular sequence of inserts/removes/moves, we don't unintentionally
+  // create more "CREATE" mutations than necessary.
+  // The actual nodes that should be created in this transaction have a tag >
+  // 105.
+  assert(mutations6.size() == 25);
+  for (int i = 0; i < mutations6.size(); i++) {
+    if (mutations6[i].type == ShadowViewMutation::Create) {
+      assert(mutations6[i].newChildShadowView.tag > 105);
+    }
+  }
 }
 
 } // namespace react
diff --git a/ReactCommon/fabric/mounting/tests/ShadowTreeLifeCycleTest.cpp b/ReactCommon/fabric/mounting/tests/ShadowTreeLifeCycleTest.cpp
index d065a696663..ab2ad89b990 100644
--- a/ReactCommon/fabric/mounting/tests/ShadowTreeLifeCycleTest.cpp
+++ b/ReactCommon/fabric/mounting/tests/ShadowTreeLifeCycleTest.cpp
@@ -169,7 +169,7 @@ TEST(MountingTest, stableSmallerTreeMoreIterationsClassic) {
 TEST(MountingTest, stableBiggerTreeFewerIterationsOptimizedMoves) {
   testShadowNodeTreeLifeCycle(
       DifferentiatorMode::OptimizedMoves,
-      /* seed */ 1,
+      /* seed */ 0,
       /* size */ 512,
       /* repeats */ 32,
       /* stages */ 32);
@@ -178,7 +178,7 @@ TEST(MountingTest, stableBiggerTreeFewerIterationsOptimizedMoves) {
 TEST(MountingTest, stableSmallerTreeMoreIterationsOptimizedMoves) {
   testShadowNodeTreeLifeCycle(
       DifferentiatorMode::OptimizedMoves,
-      /* seed */ 1,
+      /* seed */ 0,
       /* size */ 16,
       /* repeats */ 512,
       /* stages */ 32);