Only half XP for quests

Yesterday i got very weird bug, my xp from quests was halved on one specific character.
In Hellfire Peninsula instead of over 10k xp from quest i'll get 5k. Quest is stated to give me 10k in quest log, but when i talk with NPC to finish it, value stated in NPC dialogue is 5k and it gives 5k (as by numbers on xp bar). Tried multiple quests, other zones, game resets, clearing CACHE and nothing helps.
It was fine in Sunday, problem started yesterday. Any q that i had in log before yesterday will show correct value, but when returning it it will have 50% of xp, any new that i take will have half of xp in quest log.

Screenshot should help explaining more
https://i.imgur.com/JDxBAdx.jpeg

Did you set your exp to 0.5? Right click your exp bar to see, and change it back, if it was due to that.

I had no idea that option like this even exist, I must have changed it by accident.
Thanks for help