Gal not updating
By default in Exchange Online, the Address List role isn’t assigned to any role groups.To use any cmdlets that require the Address List role, you need to add the role to a role group.Although all parameters for this cmdlet are listed in this topic, you may not have access to some parameters if they're not included in the permissions assigned to you.To see what permissions you need, see the "Address lists" entry in the Email address and address book permissions topic.
Is there any way I can force a manual update of the Offline Address Book (OAB) in Outlook or reset it completely otherwise?
For details, see the “Add a role to a role assignment policy” section of Manage role assignment policies.
parameter specifies the domain controller that's used by this cmdlet to read data from or write data to Active Directory.
If this is happening, then you may notice missing, non-existent and/or incorrect entries.
Synchronizing your Outlook (cached) address book with the Global Address book may fix these discrepancies.