Quest triggered as fail but was under level to accept it.

Failed , Spiderhaunt: Kill spiders for the Lumberjacks

This doesn't tell me what triggered it as a fail.

Or how you took a quest while under its level.

Or anything else.

Gimmie relevant log snippets!

It's likely a turn-in while at the level, with the reward pushing them past the level. It still happens sometimes with quests.