there was some talk it was mainly an east coast issue.
I can definitely confirm that from Northern Pennsylvania all the way through the Northeast I had the problem. It stopped promptly when I came back into Pennslyvania and I haven’t had an issue since. I live in a motorhome and have had this AT&T plan for about a year. Started in Colorado, now in North Carolina. Thus far, only in the northeast.
I’ve replicated the problem in Minnesota, no coast over here 
Crazy that 6 months later this is still an issue and AT&T hasn’t fixed!
Word is AT&T just deployed a fix?!
Can anyone verify their connection is no longer dropping?
And what are folks finding is the best TTL to set on the Peplink? What if there is a wireless access point in between the peplink and end user device? Do I add +1?
I switched back to AT&T sim today as a test after seeing your post. I went 9 hours without an issue - way longer than before. I’ll keep using this and report back what I find after a few days
*update 12/8/2020
@mystery as an update I’m going on 30+ hours without an outage. Interesting I’m on band 2 and not 66 any more. Do you have a reference link to information about the fix from AT&T ? Thanks!
Just chatter on the AT&T forum.