I failed a combat leve the other day, so it can happen too. I was qued for a dungeon and it was taking too long, so i started to run the 5 leve challenge log entry. I finished 2 or 3, then the que popped while i was working on the next one. I had defeated all the enemies, but the timer hadnt stopped yet so it counted as a fail. I also remember farming leves in HW for chests when i needed some amber-encased vilekin for something(maybe this was relic related?). Spawn the leve, look for chests, end the leve without doing the work, spend an allowance to try again, check for chests again. It was like 100 times quicker then finishing leve, running back to ishgard, getting reward, and taking leve again. This method is also sometimes used in attempts to spawn the S rank for the hinterlands(if anyone cares about that these days).