For some reason, the healing grenade decided change sprite indexes on us and that means its locked again for all existing save files.
I couldn't figure out an easy way to unlock it for everyone so you'll have to do it manually.
If your healing grenade is locked (check under stats -> unlocks) then press F2 while in front main menu, where you can see the Tutorial and your level etc. This will unlock the healing grenade again for you, free of charge.
If you haven't unlocked it at all yet.. well, theres a free unlock for you. This will go away by next version update, so make sure you do it now.
If its not working, make sure you update your game on Steam.
Edit: Added a little check to see if you are at level 77 or higher. If you are, the fix should apply on its own.