Left act 4 cemetery boss and boss is now gone (tried reset instance)

Bug Report ID: #441354652

I was afk and also respecced character.

Went back and boss doesn't spawn.
Killed the 2 underground bosses.
Boss still doesn't spawn.

Friendly people in chat tried by asking me to join their instance. Still no boss for them or me.

Gave up.

Now report it as a bug.