One of my 4 friends got disconnected each game

We were searching as a party of four, and nearly every game, one of us would be disconnected from the lobby just before the game started, and we were replaced by a random player.

It was a different person who disconnected each time (obviously with repeats because it happened so frequently).
It happened at some point between the end of one game and the official start of another (i.e. it could happen while we were searching, while we were loading a map, or while we were choosing a playlist).
It always said that the person remained in our fireteam and on the other 3 screens, that player was visibly in the game with us. However, on their screen, they were in the main menus.
It always said that they were trying to join our fireteam (despite being listed as members already…) but it never allowed them to.
Occasionally all four of us would be disconnected at the same time.

This was after the servers were supposedly fixed.

Very disappointing that I couldn’t play a few games with friends last night because one of the four of us was always looking at a red error message.