diff --git a/src/main/java/org/dynmap/neoforge_1_21_1/DynmapPlugin.java b/src/main/java/org/dynmap/neoforge_1_21_1/DynmapPlugin.java
index b54648a0..88fd479c 100644
--- a/src/main/java/org/dynmap/neoforge_1_21_1/DynmapPlugin.java
+++ b/src/main/java/org/dynmap/neoforge_1_21_1/DynmapPlugin.java
@@ -245,7 +245,9 @@ public class DynmapPlugin
                 }
                 int lightAtten = 15;
                 try {	// Workaround for mods with broken block state logic...
-                    lightAtten = bs.isSolidRender(net.minecraft.world.level.EmptyBlockGetter.INSTANCE, BlockPos.ZERO) ? 15 : (bs.propagatesSkylightDown(net.minecraft.world.level.EmptyBlockGetter.INSTANCE, BlockPos.ZERO) ? 0 : 1);
+                    // [1.21.1] canOcclude()+isAir() replace isSolidRender()+propagatesSkylightDown()
+                    // Avoids modernfix/ferritecore lazy BlockState cache Guava LoadingCache deadlock
+                    lightAtten = bs.canOcclude() ? 15 : (bs.isAir() ? 0 : 1);
                 } catch (Exception x) {
                 	Log.warning(String.format("Exception while checking lighting data for block state: %s[%s]", bn, statename));
                 	Log.verboseinfo("Exception: " + x.toString());
@@ -254,7 +256,8 @@ public class DynmapPlugin
                 // Fill in base attributes
                 bld.setBaseState(basebs).setStateIndex(idx - baseidx).setBlockName(bn).setStateName(statename).setLegacyBlockID(idx).setAttenuatesLight(lightAtten);
                 if (bs.getSoundType() != null) { bld.setMaterial(bs.getSoundType().toString()); }
-				if (bs.isSolid()) { bld.setSolid(); }
+				// [1.21.1] canOcclude() replaces isSolid(); avoids same deadlock
+				if (bs.canOcclude()) { bld.setSolid(); }
 				if (bs.isAir()) { bld.setAir(); }
 				if (bs.is(BlockTags.LOGS)) { bld.setLog(); }
 				if (bs.is(BlockTags.LEAVES)) { bld.setLeaves(); }
@@ -913,6 +916,7 @@ public class DynmapPlugin
         }
 
         @SubscribeEvent
+		// [1.21.1] ServerTickEvent.Post replaces TickEvent.ServerTickEvent + Phase check
 		public void tickEvent(ServerTickEvent.Post event)  {
             cur_tick_starttime = System.nanoTime();
             long elapsed = cur_tick_starttime - lasttick;
@@ -1853,10 +1857,10 @@ public class DynmapPlugin
             	for (ChunkHolder ch : world.getChunkSource().chunkMap.visibleChunkMap.values()) {
             		ChunkAccess c = null;
             		try {
-            			c = ch.getLatestChunk();
+            			c = ch.getLatestChunk();  // [1.21.1] replaces getLastAvailable()
             		} catch (Exception x) { }
             		if (c == null) continue;
-            		ChunkStatus cs = c.getPersistedStatus();
+            		ChunkStatus cs = c.getPersistedStatus();  // [1.21.1] replaces getStatus()
             		ChunkPos pos = ch.getPos();
             		if (cs == ChunkStatus.FULL) {	// Cooked?
     					// Add it as known
diff --git a/src/main/java/org/dynmap/neoforge_1_21_1/NBT.java b/src/main/java/org/dynmap/neoforge_1_21_1/NBT.java
index 5aa461f8..0b4dd1e8 100644
--- a/src/main/java/org/dynmap/neoforge_1_21_1/NBT.java
+++ b/src/main/java/org/dynmap/neoforge_1_21_1/NBT.java
@@ -27,7 +27,7 @@ public class NBT {
 		}
 		@Override
 		public boolean contains(String s, int i) {
-			// Like contains, but with an extra constraint on type
+			// [1.21.1] Reimplemented type checking - 1.21 changed contains(s,i) behavior
 			Tag base = obj.get(s);
 			if (base == null)
 				return false;
@@ -93,6 +93,7 @@ public class NBT {
 		}
 		@Override
 		public String getAsString(String s) {
+			// [1.21.1] Added null safety - getAsString behavior changed
 			Tag t = obj.get(s);
 			return t != null ? t.getAsString() : "";
 		}