the web console events don't say much - just pool wasn't available. I don't see anything that looks like a reason in the Windows event logs or sw ha logs unless I'm missing something.
Honestly, I open support tickets. HA can be complicated, I've seen all sorts of issues over the years (from disk performance, to having to manually tune the settings).
well that sucks :)
The easiest way is to look at the HA tables in the Database, specifically the HA.PoolMembers table, when a server has a problem it is listed in the StatusMessage column. If that doesn't help then yes its onto logs and I'd recommend opening a support ticket.