Stuck in quest "The battle for the Undercity"

This quest-line is ending dragonblight storyline. After I spoke to alexstrasza 4-quest chain starts which change my realm. I have no access to any home city. I mean I can run around but there are no npc's which I can speak with. I am at :"The battle for the Undercity". It is 4/4 quest of this chain. After taking quest from voljin I see only this:

https://imgur.com/a/8NDO3ja

There should be a battle with some demon or something but maybe I missed that. Arthas and Sylvanas stay there and quest doesn't move forward. Help plx

Can't do that quest. Abandon the quest. Make an in-game ticket and explain what has happened, if abandoning it didn't help with the situation regarding the cities.