Ensure registration happens in order

src/main/java/com/minelittlepony/unicopia/mixin/MixinEntity.java

@@ -50,11 +50,17 @@ abstract class MixinEntity implements EntityDuck, Trackable {
 
     @Override
     public DataTrackerManager getDataTrackers() {
+        synchronized (this) {
             if (dataTrackerManager == null) {
                 dataTrackerManager = new DataTrackerManager((Entity)(Object)this);
+                // ensure lazy registration happens
+                if (this instanceof Equine.Container<?> eq) {
+                    eq.get();
+                }
             }
             return dataTrackerManager;
         }
+    }
 
     @Override
     @Accessor("submergedFluidTag")

src/main/java/com/minelittlepony/unicopia/mixin/MixinLivingEntity.java

@@ -52,11 +52,13 @@ abstract class MixinLivingEntity extends Entity implements LivingEntityDuck, Equ
 
     @Override
     public Living<?> get() {
+        synchronized (this) {
             if (caster == null) {
                 caster = create();
             }
             return (Living<?>)caster;
         }
+    }
 
     @Override
     @Accessor("jumping")