As a heads up, I don't know if Omega-Kerfus can be picked up normally, I managed to make them well after I installed the mod I believe may be causing the current issue. I'm on like day 50 or something in story mode if that helps this, and before anyone asks, it was for the purpose of picking up a freaky red device with four wheels and bring it to my garage, and that didn't even pan-out. Anyways, I found my Omega Kerfus walking around near the edge of the map after i told it to patrol back at base, so I was like "What why is it here" and then I turned it off and picked it up (I think, I was high, but I'm pretty sure I picked them up) and now it's gone, I emptied my entire inventory on the spot and it seems to have vanished even from the held items spot.
This maybe has to do with an event but I literally have no idea, I can only assume the mod had a bad interaction with the object and made it poof, as no other mods should have any interaction with the situation.
TL;DR, If you use Infinite Inventory mod, do not pick up Omega Kerfus? But also is there an event where they just disappear at some point and come back?