If a console has been used by another user prior to you working on it, it is possible the headphones have been omitted from their set-up in the previous show and as such, the console has not been set up for a user with headphones.
To quickly remedy this, do the following
Open a show hit the safe scene/OK close the show
Go to home/preferences/config
Then select both preferences and global defaults (see image below)
Now check your patching page - the patching should have returned and your headphones should work when a solo is activated.
Keywords: Pro1, PRO2, PRO2x, headphones,