I had this problem on a Nokia 6.1. I found the plug was not pushing in all the way. After a careful look I realised the jack socket was a closed space and sand or dirt had somehow accumulated in it, stopping the plug entering properly. After switching the phone off for electrical safety I gently scraped around the bottom of the socket with a fine pin, loosening debris which then shook out when it was turned upside down. Powered back on and all had returned to normal.
This may not be the answer for you but it is quick and easy and a simple fix if it works.