Avatar head goes into feet when using chair

I am having a strange problem that I have not seen anyone else talk about where the first time I sit in a chair with a new 3.0 avatar I made its head goes into its feet. I’ve made many avatars before and never had this issue but now every time I upload this avatar it does it. I thought it was probably a skeleton issue so I tried redoing the skeleton 3-4 times, constantly “enforcing t-pose” and despite my efforts every time the same thing happened. I even tried using the sample avatar skeleton without changing it and slapping on the model I made to it but it still did the head to feet thing when sitting in chair the first time. I’m wondering if this is a common glitch or if anyone else has experienced this recently. I tried a bunch of other avatars to see if they did the same thing and only one other had a similar issue except instead of its head going into its feet the whole avatar just shoots up into the ceiling the first time you sit in a chair after putting it on. I know this is kind of a small issue but it is pretty frustrating. If anyone knows anything about this I’d love to hear it, I’ll include a picture of the skeleton and the what the head to foot thing looks like in game

Sorry, never encountered this problem, i can only recommend only few general tests and solutions. You could try checking your avatar inside Unity, find proxy_sit2 and preview it in play mode to see how your avatar behaves while sitting. If it acts wrong, you can record your own animation clip to fix it, in Animator of vrc_AvatarV3SittingLayer2 controller replace proxy animations with one you made, put the controller in proper slot of VRC Descriptor of your avatar.
Also you mentioned that it acts like that first time you sit, does that mean that second time you sit it works properly?

yes second time and every time after sitting is normal which is why I find it especially odd. I will try those things you suggested, hopefully one of those can fix it.