GitLab team member here - can you share what made you want to make the move?
It absolutely wasn't my choice to go to a Microsoft product. The engineering manager has some issues with the way Gitlab does PR merge diffs or something like that. I've been pretty impressed with Gitlab. Having a deb package that runs Chef is pretty unique. While Chef is my least favorite configuration manager, it's always worked perfect when doing apt upgrades on Gitlab and it is 100% behind the scenes.