This happened to me on the CQ20 as well….the option to selct post/pre fader on my output #6 was the equivalent of ‘greyed-out’ although I could see the green which was much lighter in colour than when it’s selectable. I have no idea how it happened and tried to troubleshoot the issue with no success. The only way to remedy the issue was to do a hard rest of the mixer. Once this was done the option was restored…this seems like a bug in the system.