Wow… The AuthID that is entered in the dialog for setting up the backend is encoded into a “connection url”, so it will look something like onedrivev2://folder/subfolder?authid=abc:123.
The idea is that a service wanting to support Duplicati backups can have a button for “copy connection url” that you can paste in and have it all configured.
It should work such that the query parameters from the url override the advanced options, meaning that the override you put into the Advanced options should be ignored, as the url parameters take precedence.
I was guessing that it was an encoding issue, but since it works after you remove the advanced options, it must be something else.
It could be that it is simply the OAuth process that is unstable. I often see in the logs that OAuth fails for all requests towards a specific provider (e.g. Microsoft) for a period, and then starts working again with no change on my side.