Guild Wars 2

My group opted to save the inquest in CoE P1 for reasons I can’t fathom. In the process of killing the silver mobs, the wolf leaped into the bubble and became invulnerable. None of us could get aggro, pull him, or make him leave the invulnerable spot in the bubble.

In the end, we had to quit the run right there because we couldn’t kill him to proceed.

well if you wouldn’t try to save the little psychos :P
believe this bug has happened before, but think its one of the rarer ones, so less reported

Another good one is terrain issues in CM. Often a mob will let knocked back/launched onto a tiny rock, table, or bush. This can ruin the whole run. Had the happen in almost every dungeon at some point at leat once. CM is the worst offender though.