I have a bug where i wanted to stash a purple collectible since i was new and did not know it was (basicly) useless for my char, it instead created a "clone" of itself, wich i cannot get rid of, and all further purple collectibles i pick up, does not show up anywhere in my inventory.

Had a similar bug with a part of an artifact. I "fixed" mine by deleting the character and starting a new one. You could also try loading a savegame before you tried to stash the collectible.

I had that bug as well - it actually came back into inventory just fine when I quit and reloaded the game.