Games : "Shocking" trophy wouldn't pop in Metro Redux except with Rikar, not Hellbreath

folks:

I was playing Metro Redux on the PS4 and was grinding the "Shocking" trophy (get 30 kills with the Hellbreath) and had just started the Frontline mission when suddenly, it quit with an error CE-34878-0. I restarted the game and everything seemed normal, but after more than a hundred kills with the Hellbreath, the danged trophy wouldn't pop. I asked in a forum for some tips, and found another fellow to whom the same thing had happened. He said he got the trophy using the Tikar. That sounded bizarre, but I gave it a shot. (I wanted that trophy!) Sure enough: after thirty kills with the Tikar, the trophy popped!

Is this a known issue? I've googled the snot out of this, and haven't found anything. Is it because it's so rare, no one's uncovered it yet but the two of us?

A4 has been no help at all, as they've seemingly abandoned the game.

Thanks for any input.

Binky