OAuth2-Web Connection ceases functioning based on user account and machine

I have encountered a strange issue with FME web connections via OAuth2 which does not seem to be resolved yet.

On one of our company’s networks physical Windows 10 PC, there are three versions of FME Desktop / FME Flow installed in parallel (we need these to cater to our different customer’s needs). When I routinely tried to check and update an FME workspace, I ran into the problem that authentication with an OAuth 2 Web connection (via Microsoft 365 account) did not work anymore. At first, the web connection window took more than 40 (!) seconds to appear with the logos sometimes not even fully appearing. When I entered my credentials, it takes another 20 seconds and then gives me an error not to have found it. The credentials are tested and correct. There are no proxy connections.

Resetting FME Options has not worked, and neither has setting up the web connection completely from anew.

Tests on a different machine within the same network (but on my Windows user) could not replicate the problem, so I would assume there are some user specific config files that appear to be shot. I also tried to rename the “fme_connections.data” db in the user folder, to no avail.

to summarize, in short
-it happens with a particular user on a particular machine, but on all installed FME Desktop / FME Flow versions
-the same connection works with the same windows user on a different PC in the network
-the connection also works on the affected pc when a different windows user accesses it.

Is there any solution left apart from reinstalling all FME Versions on the affected machine?