I was on the step where I need 6+ auto rifle kills, in 4 separate matches. I noticed today where I had a match with 6+ auto rifle kills (and over 5000 points in control) did not register towards completing the step. I thought I also noticed this issue yesterday.
I thought if I abandoned the quest and then picked it back up from the terminal, it would reset the issue with the quest detecting my progress. However, now the quest line has completely disappeared, it's not in the terminal, and I can't speak to Shaxx about the quest either.
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The quest has been disabled. You don't need to do it as the step after was made available. It glitched a month or 2 ago. They probably just removed it. But it's not a big deal as you can still progress.