We are seeing the same. Made a very simple mission with just a couple of Hummingbirds, a BLUFOR rifle squad at the airprot and an Opfor rifle sqaud a bit to the west.
Two of us joined the server (no mods running on server or our systems) and hopped in one Hummingbird and ordered the AI into another. Took off in the Hummingbird, and flew around. The other guy in the Hummingbird never saw it take off. We never synced up after that.
Its a serious issue that has broken all our games over the past week.