The workaround is in the storage behavior of the params field. Ensure it's displayed on profile edit and registration. You can try hiding all the parameters using Hide Parameters under the fields Parameters tab, but I've no idea if that'll result in the issue again. Joomla handles params column storage poorly by always JSON encoding it even if it's already a string. We'll need to move the workaround to our database table object just before we save the Joomla user object. This wasn't an issue in past CB releases because in past CB releases it was impossible to hide the params field.