It seems portal.microsoftonline.com is down, this may affect OnedriveMapper users, some tenants seem to get redirected during the logon process to portal.microsoftonline.com, but many also don’t. If you’re affected, open a ticket with Microsoft.
OnedriveMapper will show this in the log: | ERROR | Error detected while following redirect, check the FAQ for help
Update: it seems only ADFS / federated tenants are affected.
Update: the RPT update command seems to have fixed the issue for most of those affected.