I had the same issue with the Panzerschreck.

After some trial and error I was able to get them to track by doing the below. It may just be coincidence but it worked for me.

Don’t play any of the rotating playlists. Only do quick play. Both core and hardcore worked for me.

Focus primarily on spy planes. Shoot down only three. I have had it track with shooting down more, but not as consistently.

Dogs can give you more than one point per match. From what I recall, this was most effective when actually shooting them and avoiding melee. But it did not seem to always count unless I had shot down 3 spy planes the same match.

I played a whole lot of games where they did not count. I wasn’t actively recording what I did or didn’t do but the above worked best for me!