Often when I unlock a red item from the random lockers, it will still appear as locked when I go to the customization screen.
I unlocked several Predator masks, like Nocturne, from the random lockers, and then I checked the customization for each of the classes (Berserker, Scout, Hunter), and all of them showed the masks as still being locked.
I even rebooted the game client, and it still showed the items as being locked. (I’m a PC player)