Its a very specific problem, but …
I started a new char, becourse i wanted to try something with Zane at Arms Race. I unlocked the Sanctuary and after clearing up the first mess on board, my char was 11 and able to enter an arms race. The loot from the first chest, which is supposed to help you getting started, can only be used from lvl 13 and above. So it was lost from the go … I was able to grab an item from another chest, but wasnt able to use that one either,
Btw … I had the same problem, when I started early into a DLC. Unless you skip the first quests until unlocking the Sanctuary your lvl is too low to use any of the loot of those DLCs.
Minimal level for any DLC is 13. You can of course play it with lower lvl character but loot wise it will be lvl 13.
if you want to jump into arm’s race immediately and use the loot from the first chest, when you start a new game you can select to start at level 13 and arm’s race (skip the intro missions and you’ll be on sanctuary, level 13, and can go directly to arm’s race). I did this with a new Zane as well.