So we did a combination of things but it is clear that odrive had linked the local Mathematics folder to the Google Shared Drive folder, even after the Shared Drive folder was renamed.
We renamed the Shared Drive folder to Mathematicsold. We created a new Shared Drive folder called Mathematics. After that we tried syncing again and although odrive allowed us to select it, it clearly wasn’t right. After thinking for a while, the folder showed as invalid on the odrive menu (under sync odrive folder).
When we right clicked on the local Mathematics folder, we had no option to remove the sync, the only option was ‘sync to odrive’. We then tried deleting both of the Shared Drive mathematics folder but this did not work as they seemed to think there was data inside (even though they were empty when going into them).
Eventually after trying to delete the folder in the local odrive folder and encountering problems, we went to sync odrive folder and clicked on the invalid mathematics entry. Odrive asked us to remove the folder which we clicked to do and this seemed to break the link.
We still could not delete the shared drive folders and I wanted to make sure we did before attempting the sync again. The next morning we tried deleting the shared drive folders again and they deleted this time.
We were now in a position to start again, there were no mathematics folders on Shared Drive and odrive had no record of them either. We then created a new Mathematics folder on Shared Drive and synced from odrive in the normal way.
Everything is fine now but yes, it was a weird situation and a lot of trying different combinations of deleting to get it to work.
My thinking is that Google Drive works in a way whereby when you tell it to delete a lot of data, it shows you the data is gone but actually it is still there. It must place the job in a queue somewhere, for processing later. Possibly to help load-balance the data centre - who knows!
Hope that helps.