Speed bug?

[Demmyale]

I was doing the heatran quest and i battled Battlemagician npc and a level 60 something drifblim managed to outsped my level 82 gyarados who is fully ev trained and drifblim used destiny bond which made me lose the entire quest. Even without being ev trained, gyarados has 1 more base speed than drifblim. Maybe its a bug with unburden but what i do know is that my gyarados has no negative priority moves so i literally cannot see a single reason as to why it would outspeed. I know nothing can be done about my quest this is just soooooooo insanely frustrating having to retrain a new pokemon and redo the quest so this is something that should probably be looked into so it doesn't happen to anyone else.