OAB not updating automatically after Exchange 2016 cross forest migration

Question

I am having an issue with OAB not updating automatically after a cross forest mailbox migration (ADMT & Preparemoverequest script)
All other aspects of migration are fine. 

However, manually downloading Address Book from Outlook works to populate addresses from the new forest. 

Noticed the Outlook clients with automatic send/receive schedule unchecked as per the screenshot below. We had it manually checked to force an Address Book download, which again worked to fix the issue. But this particular options seems to be reverting automatically quite randomly - https://social.technet.microsoft.com/Forums/en-US/d29909f1-910f-47cb-9b40-a5a6f8d13a25/outlook-send-and-receive-option-unchecked?forum=exchangesvrclients

Can't seem to find a GPO or registry key to force the option to enable automatic send/receive schedule.

Outlook should be downloading newer version every 24 hours, but problem we are having is migrated users start receiving NDR right away as the address is still being picked from the old forest. We have about 2.5k users more to migrate, so this will be a problem for migrated users. 

Any feedback is appreciated.

Answer 1