My 2012 Nexus 7 (Rooted; CM 12.1, Lollipop), has headphone jack issues. Most of the time, only the left ear will work, and sometimes I am able to get both the right and left to work. Sometimes they will both work perfectly, and it's not an issue. I know it's not the headphones, so what should I do? Thanks!
I think this is just general phone wear and tear. The headphone jack could be partially damaged due to water over time. You could get the headphone jack replaced and see how that goes for you but if the phone is 5 years old then this might be a good time for an update.