Ensure condition failed: NULL != NewGeneratedClass when trying to use an Anim Blueprint Asset ID to set a mesh's Anim Instance Class

I believe your last comment is correct. While TAssetPtr’s are pointers, I’m not even sure that they can be set to null in the same way. I haven’t used them in a while so I’m a bit rusty but I do remember this wiki page being very helpful in learning how to use them.