If that's in coal mines then it's because of leechers. Due to this weird bug you can't see people, but you see where progressive heal hits or just watch your xp. If it's 4kkk from one mob and 27k from another then I'm afraid your spot is infected with leechers who outdamage you.
I keep having this issue literally everyday, people come around because they see a tank bringing mobs and take my XP to the point where my ISS is out of MP and can't heal (I go with tank, iss and a feoh, all in paulinas so low dps). If I move away, as there are other free spots (I avoid peak hours), they follow. If I ask them to leave me alone, they tell me to quit the game if I don't like it lol. What a lovely community we have!