Sound on headphones coming from different directions. Even though I've used them for months

Jul 20, 2018
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I have been using these headphones for months now. And only recently the sound has started coming from opposite directions. Like on fortnite, if someone shoots to my left, it sounds off to my right. It's very confusing
 
First obvious question: Do you have them on backwards? I've done that on occasion. Also, can you try test tones?
What make/model of cans? Mine, for example, have detachable cables to each side and it would be really easy to put them back together wrong.

EDIT: All games and movies and suchnot? Or specific games?