AlwaysOn Availability Groups go to Resolving status
I've seen this happen a lot when folks only have one set of network cables connecting their servers - meaning, a pair of 1Gb Ethernet cables in each node, at best, and they're using those for both regular networking as well as iSCSI storage connectivity. (The fact that you're using Equallogic is a clue - I've seen a lot of those with 1Gb implementations.)

If you have any networking problems at all:


The two nodes won't be able to see each other
Neither node will be able to see the storage
Presto, no one sees a majority, and you lose quorum


Things that can cause this include:


Backup software (doing huge reads from disk while simultaneously saturating network)
Running a CHECKDB (again, huge reads from disk plus huge writes to TempDB, which can prevent the cluster heartbeats from getting through if you only have one network interface for both regular networking and storage)


To work around it:


Use separate network interfaces for regular networking and iSCSI (like a pair of 1Gb (at least) ports just dedicated to iSCSI, and nothing else)
Use faster network interfaces (like 10Gb instead of 1Gb)
Do less disk/network-intensive work (stop doing backups and CHECKDB, ha ha ho ho, but also ease up on the index rebuilds)