Hi @jarweb ,
Found the thread below which is about a similar situation. According to the discussion there, it seems that restarting MSExchangeAutodiscoverAppPool on both servers doesn't help either. So it's likely that currently educating the affected users to recreate their Ouutlook profile in case the issue occurs would be the only way to work this around.
Move mailboxes back to Exchange 2010 from Exchange 2016 cu5
"Recycled the autodisc. apppol och both Exchange 2010, no luck still same problem in Outlook clients"
By the way, as indicated in the link you shared, when mailboxes are moved from Exchange 2010 to Exchange 2016, the Outlook client can remain disconnected for "up to 12 hours", which means, it may automatically get reconnected after wating for up to 12 hours. So I am assuming if possible, you may consider testing by giving it some time and see if this applies as well when a mailbox is moved back to Exchange 2010 from Exchange 2016. If it works, an alterternative could be moving the mailboxes back in non-working hours like weekends or holidays. But still, it's not recommended to move mailboxes back.
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