So it turns out one mixin already was BE instead of TE

Therefore reverted it to BE again

src/main/java/carpet/mixins/BlockEntity_movableBEMixin.java

@@ -0,0 +1,21 @@
+package carpet.mixins;
+
+import carpet.fakes.BlockEntityInterface;
+import net.minecraft.core.BlockPos;
+import net.minecraft.world.level.block.entity.BlockEntity;
+import org.spongepowered.asm.mixin.Final;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Mutable;
+import org.spongepowered.asm.mixin.Shadow;
+
+@Mixin(BlockEntity.class)
+public abstract class BlockEntity_movableBEMixin implements BlockEntityInterface
+{
+    @Mutable
+    @Shadow @Final protected BlockPos worldPosition;
+
+    public void setCMPos(BlockPos newPos)
+    {
+        worldPosition = newPos;
+    };
+}