Hello my Ifixit family!

I have a very strange problem with a customers Iphone 6.

The left channel doesn't work while using headphones with the 3.5mm input. I've tried 3 different headsets (all known working) and I've tried replacing the headset flex(charging cable flex) to three different ones.

While using Bluetooth headset both channels are working.

Factory reset did not help.

Any ideas as to what could be wrong? :)

Thanks for all the help!