Index: oak-core/src/main/java/org/apache/jackrabbit/oak/plugins/document/DocumentNodeStore.java
===================================================================
--- oak-core/src/main/java/org/apache/jackrabbit/oak/plugins/document/DocumentNodeStore.java	(revision 1798795)
+++ oak-core/src/main/java/org/apache/jackrabbit/oak/plugins/document/DocumentNodeStore.java	(working copy)
@@ -1385,8 +1385,19 @@
             int depth = PathUtils.getDepth(path);
             for (int i = 1; i <= depth && beforeState != null; i++) {
                 String p = PathUtils.getAncestorPath(path, depth - i);
-                PathRev key = new PathRev(p, beforeState.getLastRevision());
+                RevisionVector lastRev = beforeState.getLastRevision();
+                PathRev key = new PathRev(p, lastRev);
                 beforeState = nodeCache.getIfPresent(key);
+                if (missing.equals(beforeState)) {
+                    // This is unexpected. The before state should exist.
+                    // Invalidate the relevant cache entries. (OAK-6294)
+                    LOG.warn("Before state is missing {}. Invalidating " +
+                            "affected cache entries.", key.asString());
+                    store.invalidateCache(NODES, Utils.getIdFromPath(p));
+                    nodeCache.invalidate(key);
+                    nodeChildrenCache.invalidate(childNodeCacheKey(path, lastRev, null));
+                    beforeState = null;
+                }
             }
             DocumentNodeState.Children children = null;
             if (beforeState != null) {
Index: oak-core/src/test/java/org/apache/jackrabbit/oak/plugins/document/DocumentNodeStoreTest.java
===================================================================
--- oak-core/src/test/java/org/apache/jackrabbit/oak/plugins/document/DocumentNodeStoreTest.java	(revision 1798795)
+++ oak-core/src/test/java/org/apache/jackrabbit/oak/plugins/document/DocumentNodeStoreTest.java	(working copy)
@@ -16,6 +16,7 @@
  */
 package org.apache.jackrabbit.oak.plugins.document;
 
+import static java.util.Collections.emptyList;
 import static java.util.concurrent.TimeUnit.SECONDS;
 import static org.apache.jackrabbit.oak.api.CommitFailedException.CONSTRAINT;
 import static org.apache.jackrabbit.oak.plugins.document.Collection.NODES;
@@ -3058,6 +3059,25 @@
         }
     }
 
+    // OAK-6294
+    @Test
+    public void missingLastRevInApplyChanges() throws CommitFailedException {
+        DocumentNodeStore ns = builderProvider.newBuilder().getNodeStore();
+        DocumentNodeState root = ns.getRoot();
+
+        RevisionVector before = root.getLastRevision();
+        Revision rev = ns.newRevision();
+        RevisionVector after = new RevisionVector(ns.newRevision());
+
+        String path = "/foo";
+        ns.getNode(path, before);
+        assertNotNull(ns.getNodeCache().getIfPresent(new PathRev(path, before)));
+
+        ns.applyChanges(before, after, rev, path, false,
+                emptyList(), emptyList(), emptyList());
+        assertNull(ns.getNodeCache().getIfPresent(new PathRev(path, before)));
+    }
+
     private static class WriteCountingStore extends MemoryDocumentStore {
         private final ThreadLocal<Boolean> createMulti = new ThreadLocal<>();
         int count;