The one i was on for the G43 was 10 headshots defending objective in a life or 20 of the same in a round. I had only got to 11/12 over the entire round and it ticked it'self off. I wasn't complaining as it was doing my head in ha! I think they have changed some of them now though as I've not seen one like that now.
They should just give them to everyone. They should try and do like a community based on where the entire community has to do X kills or win X rounds in a certain mode.
All the semi auto mastery 6/7 (final one) are the same. I got the 1-5 one legit with 10 defending objective HS in a life but I got the G43 one the same way you did, I definitely didn’t get 20 in a round or 10 in a life.
The shotgun one is the best, it’s 4 kills on an objective in a life and I didn’t do that either, I just got 4 kills in a life not on an objective.
Ultimately the assignments are a bit of a mess, incorrect/hidden objectives and some of the actual objectives are ridiculously difficult. I think that’s probably why the hidden cumulative option is there.
Funnily when the game first released the single player kills we’re counting towards objectives so some people did all their gun assignments on single player