Decided to give soloing Mythic Sepulcher a try. After I killed Vigilant Guardian, I immediately moved up and began killing the trash. Managed to get through all three packs plus finishing off the named maw-lich, and when I reached the teleporter, half of the NPCs which are supposed to have ran up with me started turning around and running back to the entrance of the hallway. Eventually they all did this, and now they are just standing there like none of the trash has been killed yet. As a result, I am unable to open the skip to Anduin because Bolvar is in the wrong state.
This issue is definitely new to the patch, as I’ve been in mount runs that killed that hallway’s trash much faster than I just did. The only way I will be able to work around is by just clearing all the bosses, or leaving and letting the instance soft reset.