We recently migrated from Exchange 2013 to O365 and found the owners of mail groups cannot change the membership.
From my on-premise server, I have removed the owners and added them back and even added new owners but when an owner tires to update the members, they still get the message that -
"Changes to the pubic group membership cannot be saved. You do not have sufficient permission to perform this operation on this object."
I have looked over the information in the links below, but still cannot update the memberships for any groups that were migrated. Any suggestions or help would be greatly appreciated.