Hi @jonathan.hughes,
Your observation that external enterprise connections work seamlessly while multiple database connections do not is consistent with how Auth0’s Home Realm Discovery (HRD) functions. Enterprise connections have unique email domains that allow for automatic “discovery,” whereas multiple database connections sharing a domain (or having none specified) require manual “hints” via a connection or organization parameter to function properly.
In this scenario, as you have mentioned as well, the most straight forward way of achieving this would be to use only one database connection per application/organization, as this is currently the recommended option from our side.
This is not considered to be a bug from our end, however there is also no out of the box solution at the moment, so I would highly encourage you to upvote this Feature Request - Choose a default Database Connection during an authorization request without affecting enterprise connections and leave a reply if there would be anything else to be added. This requests are closely monitored by our Product Team and a higher number of votes can lead to future implementation on our end.
Thank you!
Remus