Over 100 proven instances of this issue with my friend group! Mixture of Xbox & PC players. Consistently, without fail, we can not get into a game together. Legit stat, out of 10 queues, we get 1 or 2 games that work with all 4 or 3 of us getting pulled in. This has been happening since the beta. The issues have persisted into the finished game. Nothing seems to "make" it work or "make it not work". It is just luck.
In games that do work, when it's re-queuing from a finished game, all of our boxes will show check marks, but it still won't put us in the next game. Everytime, there are empty slots where our squad mate should have been, but it fills with a random a few seconds later.
All games up to date, all on Xbox series X's, or good computers, all fiber internet, we've played together for years in other games without issues. We are always showing in a party inside of BF6. It happens with 2, 3, or 4 people. VERY BROKEN!!!!!
Simple fix: like the 20 years of online games before you that have worked, simply don't allow a game to queue without the full party.