since i have max sigil powder and i did a faction event the sigil powder goes to missing equipment and i cant remove it or drop it or do anything with it
I had the same problem, leave game and log back in and it should be gone.
I had the same problem, and logging out thankfully fixed it (thanks RainMaker!) but this is a pretty bad bug - these can take up item slots in your missing equipment tab, possibly causing you to actually lose legendaries/uniques if you’re not keeping track. Be careful, peeps! 
can confirm bug and workaround (metioned by ryan): relogging solved the problem.