Re-rolled 'Get 50 kills or assists as Engineer' not tracking

I re-rolled one of the battle royale exclusive challenges, got the 'Get 50 kills or assists as Engineer' challenge as a replacement, and it's not progressing at all, despite me playing several games as engi. I wondered if the wording had anything to do with it so tried getting vehicle assists but that didn't seem to progress it either.

Another challenge that I re-rolled at the same time asked for 40 kills/assists with LMGs, but that seems to be tracking okay.

I play on Xbox, but I doubt that has much to do with it.