Hi Pete,
The storage and handling is a bit different now in D365. Rather than just dropping the table, you could then better delete the records only. If you do drop tables, make sure you have a backup available. Probably you can use a backup to get the table back? Otherwise try to get the table from another environment.
You can try to delete related records from the SQLDictionary table as well. If the current data is important, make a backup of the database first.