I reached the Gore nest, and failed the challenge to get 3 unique glory kills on Pinkies. Upon repeating the level, I was unable to complete the challenges because I had unlocked all of the weapon mods.
Does this mean I cannot unlock everything in the Fortress of Doom?
And as a bonus question, how many of these challenges are only doable once?
Edit: to clarify, at the end of the level it grants a Sentinel battery to use in the Fortress of Doom, if you complete all three challenges in one level playthrough. When I played the first time, I got both WeponWeapon Upgrades, but didn't complete the Pinkie Glory Kill Challenge, thus was not awarded the battery. The second time, I completed the Glory Kill challenge, but was unable to get the Weapon upgrades, since they are only "unlockable" once.