I just tested with my V4 unit and the latest stable image and the headphone works perfectly OK. I can enable/disable from the admin menu (i did it several times), adjust the volume from the audio levels screen and of course, i can hear the audio with my headphones plugged in.
Please, could you give more context about your problems? I can’t fix an issue if i can’t reproduce it.
It is ok!
I realized what happened.
If you Disable RBPi Audio in WebConf,
in Zynthian Admin settings the option Disable RBPi Audio disappears, and it is surely logic
Maybe in Zynthian Admin settings, it would be useful to have the options Disable RBPi Audio and RBPi Headphones.