i used throwing daggers in the prologue.

whenever i buy a "well balanced dagger" it will not show up in inventory.

it just vanishes.

when i craft they vanish. when i buy them they vanish.

my quick pockets are full with other stuff.

cycling through pockets does not reveal possible still equipped bugged "well balanced dagger"

so for now, i can't use that type of throwing dagger, because it vanishes in a black hole.

Let's do SCIENCE

1) Go to a merchant
2) SAVE THE GAME I am not responsible for what happens if you skip this step.
3) Strip Geralt completely naked. Including his quick pockets.
4) Double check that your daggers are not present.
5) Sell it all
6) Check Geralt's carried weight

Report the results. Unless someone knows a resolution.

weight after stripping: 0

weight after buying a single dagger: 1

does not show up in inventory and is not selectable in any way.
well, that proved they are not actually vanish, i just cant interact with them once they are in my inventory...

Does not show up.

I assume you have taken "Dagger Throwing" in the Training Tree?

yes

Sounds like a genuine bug.

To hazard a guess, there may be a hidden "pocket" they end up going into. Maybe some remnant of an inventory slot for daggers that they removed.

i think i had daggers dissapear as well once, but whatever for me

don't have the dagger throwing skill yet, so i didn't care

that was actually the exact next quest step i'd have to do.
I droppped my stuff plus the obviously invisible dagger (which i specifically bought first) in the chest.
Did the quest part, left the area and when picking up my stuff from the chest again... voila, the invisibility curse was removed from my well ballanced dagger. :3

you, sir, just saved my day. ^.^