Standby shows as offline in HA pair in version 12.1.2

I had this exact situation happen in 12.1.3 on a Viprion pair. Doing a bigstart restart sod on the standby guest didn't have any effect, but doing it on the active guest (the one reporting the standby unit as offline) fixed the issue but I did experience a bit of strange behavior:

I'm using vCMP and I have two guests with LTM running on both. Both had the same situation. When I restarted the sod on guest A, a failover happened and caused the standby guest A to go active. When I restarted the sod on guest B, there was no failover. Any ideas of why guest A failed over?