--- a/net/minecraft/server/level/PlayerChunk.java
+++ b/net/minecraft/server/level/PlayerChunk.java
@@ -28,6 +28,10 @@
 import net.minecraft.world.level.chunk.status.ChunkStatus;
 import net.minecraft.world.level.lighting.LevelLightEngine;
 
+// CraftBukkit start
+import net.minecraft.server.MinecraftServer;
+// CraftBukkit end
+
 public class PlayerChunk extends GenerationChunkHolder {
 
     public static final ChunkResult<Chunk> UNLOADED_LEVEL_CHUNK = ChunkResult.error("Unloaded level chunk");
@@ -58,9 +62,9 @@
         this.entityTickingChunkFuture = PlayerChunk.UNLOADED_LEVEL_CHUNK_FUTURE;
         this.blockChangedLightSectionFilter = new BitSet();
         this.skyChangedLightSectionFilter = new BitSet();
-        this.pendingFullStateConfirmation = CompletableFuture.completedFuture((Object) null);
-        this.sendSync = CompletableFuture.completedFuture((Object) null);
-        this.saveSync = CompletableFuture.completedFuture((Object) null);
+        this.pendingFullStateConfirmation = CompletableFuture.completedFuture(null); // CraftBukkit - decompile error
+        this.sendSync = CompletableFuture.completedFuture(null); // CraftBukkit - decompile error
+        this.saveSync = CompletableFuture.completedFuture(null); // CraftBukkit - decompile error
         this.levelHeightAccessor = levelheightaccessor;
         this.lightEngine = levellightengine;
         this.onLevelChange = playerchunk_a;
@@ -72,6 +76,16 @@
         this.changedBlocksPerSection = new ShortSet[levelheightaccessor.getSectionsCount()];
     }
 
+    // CraftBukkit start
+    public Chunk getFullChunkNow() {
+        return (Chunk) this.getChunkIfPresent(ChunkStatus.FULL);
+    }
+
+    public Chunk getFullChunkNowUnchecked() {
+        return (Chunk) this.getChunkIfPresentUnchecked(ChunkStatus.FULL);
+    }
+    // CraftBukkit end
+
     public CompletableFuture<ChunkResult<Chunk>> getTickingChunkFuture() {
         return this.tickingChunkFuture;
     }
@@ -86,7 +100,7 @@
 
     @Nullable
     public Chunk getTickingChunk() {
-        return (Chunk) ((ChunkResult) this.getTickingChunkFuture().getNow(PlayerChunk.UNLOADED_LEVEL_CHUNK)).orElse((Object) null);
+        return (Chunk) ((ChunkResult) this.getTickingChunkFuture().getNow(PlayerChunk.UNLOADED_LEVEL_CHUNK)).orElse(null); // CraftBukkit - decompile error
     }
 
     @Nullable
@@ -134,6 +148,7 @@
         if (chunk != null) {
             int i = this.levelHeightAccessor.getSectionIndex(blockposition.getY());
 
+            if (i < 0 || i >= this.changedBlocksPerSection.length) return; // CraftBukkit - SPIGOT-6086, SPIGOT-6296
             if (this.changedBlocksPerSection[i] == null) {
                 this.hasChangedSections = true;
                 this.changedBlocksPerSection[i] = new ShortOpenHashSet();
@@ -208,8 +223,11 @@
                                 PacketPlayOutMultiBlockChange packetplayoutmultiblockchange = new PacketPlayOutMultiBlockChange(sectionposition, shortset, chunksection);
 
                                 this.broadcast(list, packetplayoutmultiblockchange);
+                                // CraftBukkit start
+                                List finalList = list;
                                 packetplayoutmultiblockchange.runUpdates((blockposition1, iblockdata1) -> {
-                                    this.broadcastBlockEntityIfNeeded(list, world, blockposition1, iblockdata1);
+                                    this.broadcastBlockEntityIfNeeded(finalList, world, blockposition1, iblockdata1);
+                                    // CraftBukkit end
                                 });
                             }
                         }
@@ -275,7 +293,7 @@
         this.pendingFullStateConfirmation = completablefuture1;
         completablefuture.thenAccept((chunkresult) -> {
             chunkresult.ifSuccess((chunk) -> {
-                completablefuture1.complete((Object) null);
+                completablefuture1.complete(null); // CraftBukkit - decompile error
             });
         });
     }
@@ -290,6 +308,30 @@
         FullChunkStatus fullchunkstatus1 = ChunkLevel.fullStatus(this.ticketLevel);
         boolean flag = fullchunkstatus.isOrAfter(FullChunkStatus.FULL);
         boolean flag1 = fullchunkstatus1.isOrAfter(FullChunkStatus.FULL);
+        // CraftBukkit start
+        // ChunkUnloadEvent: Called before the chunk is unloaded: isChunkLoaded is still true and chunk can still be modified by plugins.
+        if (flag && !flag1) {
+            this.getFullChunkFuture().thenAccept((either) -> {
+                Chunk chunk = (Chunk) either.orElse(null);
+                if (chunk != null) {
+                    playerchunkmap.callbackExecutor.execute(() -> {
+                        // Minecraft will apply the chunks tick lists to the world once the chunk got loaded, and then store the tick
+                        // lists again inside the chunk once the chunk becomes inaccessible and set the chunk's needsSaving flag.
+                        // These actions may however happen deferred, so we manually set the needsSaving flag already here.
+                        chunk.setUnsaved(true);
+                        chunk.unloadCallback();
+                    });
+                }
+            }).exceptionally((throwable) -> {
+                // ensure exceptions are printed, by default this is not the case
+                MinecraftServer.LOGGER.error("Failed to schedule unload callback for chunk " + PlayerChunk.this.pos, throwable);
+                return null;
+            });
+
+            // Run callback right away if the future was already done
+            playerchunkmap.callbackExecutor.run();
+        }
+        // CraftBukkit end
 
         this.wasAccessibleSinceLastSave |= flag1;
         if (!flag && flag1) {
@@ -341,6 +383,26 @@
 
         this.onLevelChange.onLevelChange(this.pos, this::getQueueLevel, this.ticketLevel, this::setQueueLevel);
         this.oldTicketLevel = this.ticketLevel;
+        // CraftBukkit start
+        // ChunkLoadEvent: Called after the chunk is loaded: isChunkLoaded returns true and chunk is ready to be modified by plugins.
+        if (!fullchunkstatus.isOrAfter(FullChunkStatus.FULL) && fullchunkstatus1.isOrAfter(FullChunkStatus.FULL)) {
+            this.getFullChunkFuture().thenAccept((either) -> {
+                Chunk chunk = (Chunk) either.orElse(null);
+                if (chunk != null) {
+                    playerchunkmap.callbackExecutor.execute(() -> {
+                        chunk.loadCallback();
+                    });
+                }
+            }).exceptionally((throwable) -> {
+                // ensure exceptions are printed, by default this is not the case
+                MinecraftServer.LOGGER.error("Failed to schedule load callback for chunk " + PlayerChunk.this.pos, throwable);
+                return null;
+            });
+
+            // Run callback right away if the future was already done
+            playerchunkmap.callbackExecutor.run();
+        }
+        // CraftBukkit end
     }
 
     public boolean wasAccessibleSinceLastSave() {