For me I don't think it's meeting fatigue, I have about the same amount of meetings as before. But I also noticed a similar productivity spike. Unfortunately what I think is happening is that we are using up a built-up "social capital" from when we were in the office together. Many of the people I know to ask for quick questions/favors I know because of hallway/lunch conversations. As new remote devs rotate onto my team I feel the team is becoming more impersonal and I am more reluctant to ask them things or help them. And likewise I think they are less likely to ask for help to get unblocked, than they would be in office.

But FB people ops (or beyond) aren't stupid and hopefully they can come up with ways to intentionally replace this. Won't be the same but something is needed and will be better than nothing or ad-hoc.