If you have two parts, and they’re connected via surfaces (Eg. Welds, inlets etc.), and one of the parts is rotated (Even though it’s touching the surface), the joint will break.
Repro:
Create two parts, set all surfaces to “weld”. Make both parts cancollide true, and unanchored.
Put one part on top of the other part. Rotate the part on top.
Play the game, the joint won’t work.
Edit: I should clarify, it’s only when the rotation on the Y axis isn’t the same as the part below it (Eg. 0 and 45)