To be fair is your Vega64 is anything like my GTX 1080, it is bored as heck running vrchat.

I get ~25% gpu usage normally.

I think its an isolated issue or its not really related to vrchat

I can help you if you give me more info

is it only vrchat?

is the gpu downclock'ing?

does the steamvr profiler show any strange behaviour?

have you tried using mods for unlocking fps? (warning: ALL mods are bannable so keep that in mind even if the devs dont care that much)