I've been having this issue for the past two days now, all accounts sync fine except for my Gmail account. I takes a long time to sync, it often fails to sync, and my phone sometimes triggers up a warning that AquaMail is draining my battery (it's not literally draining my battery, but it's always trying to sync in the backgeound).
Tried updating AquaMail, tried re-adding` my gmail account, tried playing with gmail/Android settings, no go so far...
Hopefully it is on Google's end,.