Troubleshooting DAG database failover root cause

Hi Experts - I recently added a second exchange server at an offsite datacenter.  This server has the client access, hub transport, and mailbox server roles installed.  The two Exchange servers are in a 2 member DAG with the witness server setup back at my office with the primary exchange server.  Most of my Outlook clients are here in the main office with me so I have the active databases here set with the highest priority.

I've had several database failovers take place at night and have had to fail them back to our main office in the morning.  I'd like to try and determine why they are failing over and why they don't fail back since this side has lower value activation preference.  Many thanks in advance for any tips!