If you leave a game and press quickplay, theres an extremely high chance you quickplay into the last game again.
I’ve learned to pick a mission I like after dc’ing a mission for any reason.
Or pick a mission first and use quickplay if there is a dc.
Also time matters. If you quickplay late night with less players then theres an even higher chance of rejoining the same few games. (Few for the time/usual average)