Just being in some worlds with a 3.0 avatar causes extreme glitching in rapid succession. When looking at the debug menu, you can see the Grounded parameter is freaking out, between the values True and False.
We noticed it happens less on solid box mesh, apparently happening the most on mesh colliders. It can also happen on slopes such as stairs.
It also affects 2.0 avatars if you were glitching in a 3.0 and swap avatars. You need to rejoin to fix it.
This is a video showing the rapid flickering of the value and my model in-game.