I just finished a game of Big Team Slayer with a KDA of 14.6, and in the post-game stats it did not indicate that I had progressed at all in the “Bulldozer” Commendation (Finish with a KDA over 8 in any Slayer gametype in matchmaking). At first I thought that perhaps I had completed it without remembering, but I checked and it was 13/15, 4/5. Just bringing up this issue.
I had this issue with the Watcher Slayer and Hunter Slayer ones. I didn’t kill any of them and it worked. Can’t really help you though, sorry.