Low level tanks often don't receive any gear when open invasion chests, only shards. This bug is still up, and I don't think it will be fixed before the invasion's end.
Changing your specialization doesn't necessary. Just right click on your character portrait, and choose a non-tank loot rule under Loot Specialization. The only drawback of this solution, you couldn't receive the correct weapon.
So instead, you should do the following: Hide in a safe place, and stay passive whole time. Never open any chest during the event, wait until you are back to the normal phase. I hope it helps!