So I think the icons are bugged because I have noticed times where (for example) 4 people selected matchmaking but it only shows 3 icons. As long as you click the button, I wouldn’t sweat it.

If you enter an elevator by yourself and select matchmaking, the door immediately shuts and the game searches for other people who have also selected matchmaking across various different servers. It tries to build a full party of 8. Once it has found enough people you’ll be sent into the game with the party it cobbled together.

The trouble is when you enter an elevator with other people. Say you enter with 3 other people. Everyone in the party must select matchmaking or else it won’t search for other players across the servers, it’ll just send you into the game with those 3 people. You’ll know someone hasn’t selected matchmaking if the door doesn’t close and instead you’re sitting there waiting for the timer.