Updated to Jaspersoft Pro 5.6 using the overlay installer on AWS Amazon linux. Went well, established reports all seem to run well. Ad hoc editor is working fine. The data source is AWS RDS MySQL.
When trying to work with the Domain Designer, it errors on save or when using Check Design. This happens when creating a new domain or editing an existing domain. The existing domains work fine in the ad hoc editor.
Stack trace is attached. The error is the same for any domains.