Hi,
Same thing happened just now.
Refer to Black charctor screen after disconect
It’s been happening last 3 days, and when it happens all my battlenet friends experience the same issue - so I know it’s just not my PC.
Either the game kicks you out and you log back in with black screen, or if you remain in game everything begins to lag and can’t interact with NPC anymore, with only chat working.
Refer to OCE realms Frozen and Major lagging/disconnections on Oceanic realms atm
As this happens off-peak for US, and peak for us in OZ, this remains for a while before it gets fixed