This is an issue that’s recently started happening (I think it started happening on the patch before this one), and I can reproduce this 100% of the time. @32bitPC has told me about himself having the issue as well.
I noticed this issue when I was testing accessories with models in them. I weld the model together, then weld the model’s primary part to the accessory’s handle. I then add it to the character, then unanchor the accessory’s contents. Shortly after, the character has some weird issue occur (I haven’t quite nailed down exactly what it is yet) that results in the CFrame of their body to be unreal (NAN).
I have found this MUCH more evident in accessories than models, though 32bitPC reported it happening in models as well.
Edit: I was using R15, he was using R6. That may be the difference.
There’s a READ ME script in the workspace of the repro, it goes over the chat widget I set up so you can easily demo each issue.
After you attach the model or accessory, start walking around and jumping. It should occur fairly quickly.
Repro.rbxl (23.9 KB)