I've noticed while leveling in BfA that i'm having to close and reopen vendor windows a few times if I have a load of a grey items in my bags. Unsure what the specific cause is as in theory this didn't change with BfA.

I do use BaudBag. Maybe that is a cause so will test without that first.

I'm having the same issue !! I was doing the Vol'dun side quests, bag full, i summon my mammoth and have to click 3 times to sell all the greys. And i don't use any other addon for this.

Well that at the very least confirms it. I'll be taking a look.

Assume this is still a valid issue, may take look into it on my fork, otherwise for now since I also use the recommend add-ons besides Story I could just toggle auto sell-off in this and on in baudbags,