Buffer Underflow

I'm unsure what "buffer underflow" actually means and googling it just opens a can of worms i can't understand. But it seems to be effecting a lot of players atm.. Is there something we can do to fix this or it something GGG need to fix?

I just had this now in act 3 in the jungle area said "buffer underflow" and now trying to log in each time it says the same thing and force closes my game. Have you found a way to fix this?

All i did was verify integrity on steam, and restart my pc.
That somehow fixed it for me specifically, i've heard of cases where that isn't the case