3 times in a row I fought 1 enemy and got into combat bug after killing him.
I had to hearthstone each time
Why?
It really depends on what you mean by “combat bug”, I am guessing it is you are staying in combat after killing the opponent, but you will want to provide detail to any bug report. Like what area you are in, etc. It could be there are mobs in the area that you can not see, maybe under the ground, it could also be a ability targeted a critter in the area, but missed and sent the critter away from the area but kept you in combat. Usually you can run from the area and it should reset.
You can also try a UI reset to make sure there is no UI corruption causing issues as well,
Blizz, Puleeeeze! fix the “you are in combat” bug that has been around for the last few expansions. it is getting worse! I get the you are in combat bug on a regular basis and I can’t get out of it. I kill things, I exit the game, reload UI, nothing seems to bump me out. At least allow us to use the flight whistle while in combat.