@bumoverflow The idea that it worked on Private window and New Profile often means extension is causing a problem. 99.9% of the time, it’s what resolves. I know you mentioned disabling extensions, but did you truly disable all of them? If so, might need to go one step further and remove them entirely.
The other 0.01% of issue would be clearing cookies, site data, and all. So those would be my two suggestions to attempt right now. To clear cookies and site data, go settings → privacy and security → clear browsing data → basic tab → All time for time range → then make sure Cookies and other site data is selected. Should look like below (don’t have to do the cached images and files, but may as well):
Things like VPN, proxy, antivirus, firewall, etc shouldn’t play a part. If they did, usually would effect all profiles. Exception, of course, is if you have one of them running as an extension or something. But might be other thing to test.