Now, very simple I’ll just explain what happend, you might had a similar situation. In my opinion it’s a bug, I could be wrong.
I dont use any mods.
I started a new settlement, with a trapers knife AND a sword.
I promoted a footman before I tried to promote the traper, usually i go for a traper very first… but i forgot.
As I realized we need a trapper I was actually able for a promotion, but nothing happend after the claping sound.
Well finaly as my very first footman died later on in the game he droped that trapers knife we were missing before.
strange enough for me therefore he had the choice of knife or sword. and after he took it i still had the option to promote a traper wich didnt work.
ty for reading