Level 50....Gladiator?

[Xaphire]

I lost threat to a DRG

This either happened in the first six seconds of a fight, or the DRG was attacking the wrong target in a multi-pull, or you didn't have defiance on. The only time I've seen a tank (PLD or WAR) lose threat after the first 15 seconds or so into a fight was to a WHM spamming Medica II and Cure III to pull threat deliberately.