Unable to stay connected to Windchill

I have an open PTC case but wanted to see if anyone has any experience on this.

I have 1 user who can no longer connect to Windchill from a specific PC. Anytime he tries to connect he gets an error that the server is offline. It will attempt to go online and fail. Sometimes even giving the "server is now available" but quick to go back offline. Over the past month it's been a progressive decay from occasionally happening to always happening. Clear participant cache at one point got him a day's worth of work before going offline again, then an hour, then minutes. Same with clearing caches/appdata. It works sometimes, but not forever. Methodserver is showing it as Creo disconnecting, along with socket write errors.

I've purged caches, appdata, Creo Parametric program files, everything I can think of that belongs to Creo. Firewalls are fine. Network appears fine.

I can log in on his machine, works fine. He can log onto other machines, works fine. Browser works fine.

PTC is pointing me towards fiddler, but I'm not really comfortable running that on someone else's machine. Especially when the steps say "click the check box that has (not safe) next to it"

Any thoughts? I feel like I've tried everything.

Creo Parametric 2.0 M220 with Windchill 10.2 M030 (also happened on M020). We do have single sign-on, but I've also tried our administrative bypass with no change.