We had a similar issue. I received this email from them and it seems we needed to re-approve the API permissions...
You need to go to gsync.wonde.com/reconnect and login as a super admin to re-approve the API permissions from Google. We have lost connection with your Google Workspace at some point and that's why you're unable to run syncs.
Once this was reconnected we could sync our classes... took a few days to get this response out of them as well as they are pretty busy with Google issues at the moment and there was no indication this was an issue in the UI. Don't know if it will fix your issues but it may be worth a try
