Hi there,
I've got the same problem, right ear doesn't work without any incident / any hurt.
I've tried thousand things, update mobile app, change settings, reset using the app, try BT or Wire, at the end I was ready to open it !
Finally... I reset all the settings manually and it works ! I read that you already reset the settings but did you try to do it manually ?
(as it mentionned at the end of the user manual)
***Resetting the headphones to the factory default settings/Reset***
1. Switch the headphones off
2. Press the voice assistant button for 4 seconds (near the ANC button)
https://www.manualpdf.in/sennheiser/pxc-550-ii/manual?p=35
Hope it will help
Thanks