Thank you for reaching out. I can see your account status is currently on our free explorer plan. When a client shares you a map from a paid subscription, unfortunately, you are not granted those paid privileges as far as exporting. You are able to view the map and also the annotations.
If your customer adds you as an organization member, that is different. That will allow you full access.
You may have been on our Pro Trial during those times you were able to export the maps and now it has expired.