When me and my friend completed the scorpion waves we were both down and it finished but they didn't appear in my inventory when I went back they weren't there and also when we recovered our backpacks they still weren't there and unfortunately I didn't save the game so I couldn't re do it. 

Any tips or are they completely lost?

Hi, You usually have backups that you can select when you start the game. You'll find multiple save games there. You can then select the appropriate one

It's a recipe you unlocked.  You need to craft them.