Left ear not working on normal mode, but works on 7.1

Left ear not working on normal mode, but works on 7.1
Hi , i just got home and wanted to play something but i noticed left ear stopped working , when i press the 7.1 it does. but i dont like that for listening to music etc. I have a headphones holder so i am not someone that throws them on the desk everytime he goes away. The jack is not bent, everything looks as new. Any ideas what it might be?

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