Hey everyone, we do have plans to label schematics to make it clear whether or not it is already known by your character, but don't have a timeline as to when this change will take place. It's definitely something we want to add to make schematics easier to assess!
This also happened to me but it was with a CREW-SKILL MISSION (UnderWorld Trading). I purchased 2 from the GTN and used 1 and that woked fine and then I tried to use the 2nd. I consumed it but no sound effect on msg in chat bar about my mission and no option for the mission when I check the UWT options.