The following issue has been identified and subsequently replicated by MYOB Support in EXO Business versions 2018.4 onwards.
Before upgrading your clients please take into consideration the following issues especially if the site has specific requirements in these areas.
As always we recommend that thorough testing in a non-live environment is undertaken before commencing an upgrade.
Issue
If a new connection to a 2018.4 or newer database is created then the Exo Business Services program will be unable to see it.
Workaround
Create the connection in Exo Business 2018.3 first then upgrade the database to a later version.
Resolution
Attached to Problem ticket 168435761698 for resolution in a future release.