Challenges not unlocking upon completion (PS4)

I am having troubles with some of the challenges.

Mercenary: Demon of the Skies - I started a thirty second timer and stayed in the air for the entire time and a few more seconds. Nothing.
note: don’t go too high or it plops you right back tot he ground

MUL-T: Gotcha!
Pretty sure I killed the imp overlord w the PA but that said there may have been a bleed or something else. I would say I did it, but it is debatable

Engineer: 100% calculated - nuked a boss in about 3 seconds. Had 13x armour piercing to help it happen. Should have popped.

Are there some bugged challenges? Do they need specific difficulty? It’s a bit frustrating.

Looking for some help