Since they have meetings rotating between multiple continents, the WG chair probably already knows about all participants for which this is an issue. They explicitly mention being aware of this problem in their announcement, but that they deem it less critical right now.

Yes it can if you are referring to non-citizens.

I'm a US citizen and routinely fly to various out of country locations including somewhat suspicious places like Belarus (no longer need a visa to go there for short trips) and have never had a problem re-entering. It probably doesn't hurt that I'm a middle-aged white guy, though.

Yes, but it's better than the alternative.