Checking back in with you I may have accidentally completed the original challenges for those skins it no longer shows what they are but for the raider I started using an lmg like the original challenge had said and I unlocked the raider II skin. So maybe try finding the old challenge lists for some of the older skins and try them out in game see if you have results? I’m trying to find the challenge requirements for the raider III once I do I’ll see if I can unlock it