I've been having the same issue with Office 365 products when running NordVPN - Outlook won't connect to Office365 mail boxes, One Note won't synch changes, Excel and Word file changes are not saved to cloud folders, and OneDrive stops synching files. I've
turned off CyberSec in NordVPN and set it to use UDP - and this doesn't solve the problem. consistently.
One fix which worked for me is to change the DNS settings of my Wifi adaptor to use Google's DNS servers - searching for "Office 365" at the
support.nordpvn.com website will provide a step by step instruction guide on how to do this.