If they're in a loadout, they can't be sold.
If they're in a loadout, they can't be sold.
^This is usually the cause.
It happens to me that I have 3 mods I cant sell. I dont have any loadout, they are not locked.. they are white 3 dot mods lvl 15 that show nowhere but in the pool to add to characters.. of course I dont use them, tried to equip, unequip.. also even tried doing a loadout and then deleting it.. but to no avail.. I just have those 3 running around :P
They could be bugged due to a mod update ages ago. Unfortunately, we were never able to remove them safely, and since it is only a low number we decided to leave those untouched.