Hi All,
I have just been working on this issue, what fixed it for me was to completely delete the connector, Data (on the left) -> Connections -> three dots next to the excel online connector and delete. It warns of the flows that are using it, make a note and delete the connector.
Now open a flow that was using it and go to the action with the issue. Click the three dots in the top right and instead of clicking on fix connection, create a new one. Sign in as normal. Then test again.
Hope this helps.