SSL certificate change in gmail

[Thud Hardsmack]

About a week before Thanksgiving I received the Oct security update for Android 6 on my Verizon G3 (VS 985), and shortly after that it started failing - it went into round the clock bootloops except for the occasional catch and it would boot fully, only to display "No Service" though my SIM was installed. Tapping that would send it back into bootlooping. After 5 FDR's and no joy I had Verizon solve my problem with a replacement. For the most part it works even better than before, but there's just one problem I can't live with: Aquamail is reporting SSL certificate change: imap.google.com:993 on all my Gmail accounts in Aquamail. I have the Gmail app installed as well for use with Google Now and it's not having any issues.

What I need to figure out is whether this is:

being caused by Aquamail - it also had a couple updates and I didn't have any warnings for the first few days after restoring to the replacement G3. To be fair, I get the warnings and sometimes the app works anyway. I've tried deleting the accounts, and then the app as well, didn't fix it.

Being caused by Google - I've read this has happened elsewhere and not specific to Aquamail. But, why Aquamail and not Gmail on the same device?

By the latest security update - this is truly when everything went wonky.

Or something else entirely. (Seriously hoping not)