We are currently in the process of migrating our users from Office 2016/2019 clients to the new Office 365 Client Suite to get them ready for Microsoft 365.
Some of our users (but not all of them!) are now experiencing problems when they are trying to access Documents that are stored in our local SharePoint 2016 environment.
Upon opening a Word/Excel file in their office application, they are receiving the following message:
"Unable to open https://url.com/sites/abc/xyz.docx"
One weird thing i have noticed is, that it ALWAYS works, when i try to debug it inside Fiddler and Fiddler is authenticating to our SharePoint.
After some digging through the registry, i found that it works exactly once after i delete the key with the url of our SharePoint WebApp in HKEY_CURRENT_USER\Software\Microsoft\Office\16.0\Common\Identity\ServiceAuthInfoCache\CredStoreKeyToAuthScheme
Office just recreates the key and it stops working until I delete it again.
Any advice on how to find the cause would be greatly appreciated.