Didn't get the credit for completing the story in co-op on TVHM

So, I was playing with my brother all the time: we did the whole story + side quests on normal mode and then decided to finish the story on TVHM just to have access to every zone.

Although everything works fine on normal, as soon as I change to TVHM, I have to go through the campaing again. My brrother was the host all the time and he has it unlocked, but not me.

Is this a bug? Not gonna lie, I don’t find myself doing the story again any time soon without some QoL changes, but since I already did it, I kinda want to have it unlocked.