recon mods only go into the slot when you see recon data as a reward from the boss. The mod simply gives additional recon data on top of the base reward. So you will need to check the rewards first. It might be a weapon, an armor piece or recon data. Which one is available seems to be random after each hunt. You have to actually do a hunt for a different reward for new rewards to show up and then hope it will be recon data next.