I don’t know if this has also happened to you, but i recently had two instances in which i had an active challenge about getting 20 kills in team slayers matches in pvp and also had challenges related to other game modes only playable through quick play queue, like CTF, so i simply queued for quick play since then i could end up in either a CTF or a slayer match. I played the team slayer matches, got the kills but the kills didn’t count for the challenge after finishing the match. They would only count for the challenge if i get into the match through the dedicated team slayer matchmaking queue.
This issue is specially frustrating in my second case in which this happened, in which i simultaneously had a challenge that required me to play matches through quick play (get cumulative score in quick play matches in pvp), because I artificially couldn’t progress both challenges simultaneously by playing team slayer through quick play, which translated into unnecessary grinding
