Upon uploading these two custom packs - one for behavior, and the other for models/textures (co-dependent). I'm seeing the attached error message. It flashed for a couple frames, and then was replaced by a "Some of the selected content could not be applied" message.

I haven't been able to find any references to this error message specifically, or diagnose the specific issue with these packs. They seem to work perfectly fine on my local server.