Do I take it from your timings that there was aIt looks like that to me.
First thing in the morning Pacific (UTC-0800) I found that the copy of Thunderbird I'd left running overnight was no longer authorized to access my Gmail accounts. My receipt of messages from Groups.io via those accounts was not interrupted at that time.
In the mid-afternoon my more active Gmail address went on Bouncing status and I missed the receipt of several messages in both GMF and Beta. I also missed the Bounce Probe (that I assume was attempted) and only discovered my bouncing status because I visited the web site.
In GMF's Activity log the bouncing of Gmail accounts began around 2:45 pm Pacific and continued until about 3:41 pm.
The possible connection between the two events is that the bounce reason was "The email account that you tried to reach does not exist". Not exactly an authentication issue (inbound rather than outbound), but still related to my Gmail account identity.