Some users have reported issues with logging into SOGo even when using the Cloudron email after the update. This is most likely because you are using an older version of SOGo. The old SOGo app was deprecated ~6 months ago as part of the 2.3 release and is not supported. Please move to the new SOGo immediately.
Install the latest version of the SOGo app (from the appstore) in another location/subdomain. You should see your email when logging in with email now.
If you use calendar/contacts in old SOGo, you can migrate it to the new SOGo using the guide at https://cloudron.io/blog/2018-12-05-carddav-caldav-migration.html
If everything is satisfactory, you can just uninstall the old SOGo.