I experienced at some point when I suddenly dc’ed while inside an instance boss battle. My quest is still active but when I go to the designated place to trigger the boss fight it does not trigger as intended.
My temporary solution to it is to reconnect, abandon the quest and restart. In some cases when I can’t abandon the quest even if I’m clicking abandon several times, I close the game then reconnect then it’s back again.
There are also many cases where I suddenly dc at many instance boss fights for reasons unknown.