Processes in Microsoft 365 for setting up Office apps, redeeming product keys, and activating licenses.
After coming back to PIA after not using any VPN for a year, I noticed the same problems that the OP and many others were having. I changed from UDP to TCP. Excel wanted me to sign into Office 365 again. One Note 2016 wanted me to sign in again also. It's only been 30 minutes but everything is working well so far.
It didn't work for me (with NordVPN), but hopefully it will work for you. The only thing that has worked for me has been to add my gateway as the default gateway in the Tap-NordVPN Ethernet adapter - per Mac Wheeler's post. It still passes the tests at IPLeak.net so hopefully it works AND I'm still protected by the VPN.
Paul