I'm asking for a friend because he doesn't think anyone will help.
He recently installed a new motherboard, gpu, and cpu. Here is his message posted on the VRChat forums for here.
Hi, I upgraded my CPU (and my motherboard and RAM as well) from an AMD FX-6300 to a Ryzen 5 2600. Everything's been running a lot smoother except for VRChat, which seems to be locked at 13 fps at all times, even in very simple worlds, never going above or seemingly below it. I've tried clearing the cache, deleting my PlayerPrefs, reinstalling the game, reinstalling my graphics drivers, installing chipset drivers, disabling hyperthreading/SMT in the BIOS, setting vrchat.exe's process priority to high, and fiddling with its core affinity, but none of that's worked, and I'm at a loss here.
If this helps at all, here's VRChat's performance without hyperthreading enabled: https://i.imgur.com/bQzHQaM.jpg
Here's a recording of it as well, using NVENC so it doesn't take a significant amount of performance from VRChat. https://www.youtube.com/watch?v=yTXEmubISAU&feature=youtu.be