I have many AG on SQL 2012. I get this message a few times a day. It fix itself withing 60-120 seconds.
A connection timeout has occurred on a previously established connection to availability replica 'zzz' with id [6A004D27-B391-42BA-A3F7-BDC8EB570C4F]. Either a networking or a firewall issue exists or the availability replica has transitioned to the resolving role.
When this occurs there is no special error in the cluster and no other application (i.e. exchange) is reporting any communication error.
Recently I realized that it happens almost every day at 3:30 and 15:30 but I don't see anything special around that time (no heavy work neither high iops).
Where could I look for the cause of the disconnections?