An ongoing issue with a customer of mine is that they have share point online. However due to sync problems with the one drive for business we went with drive mappings to libraries.
The drives are mapped with the unc path method and work ok when they are working. But every so often and randomly they will get a red x on the drives and have to logon to sharepoint online and open the library and then open in explorer. This restores the connection. But this can happen a few times a day. Even though they have told IE to keep them logged in to the portal. Then it can be a week before it happens again.
Webclient service is in automatic and started. The SharePoint url is in the trusted sites in IE. Keep me signed in is ticked on the portal.