You might be killing your analog switches with your opamps.
You have the nominal DC level of the opamps set at 6V by resistors R2 and R3. That nominal DC level, plus the peak of your AC signal, is feed to pin 4 of your switches, which have an absolute max voltage of 6.5, so if you have 0.5V peak AC you are exceeding their spec.
Ideally, you set the DC bias to one half of the operating voltage of the analog switches, and make sure that the peak to peak AC signal does not drive that signal past it's Vcc or ground. Ideally giving it a good margin.
The simplest way to change the DC bias voltage would be to run your divider from 5V instead of 12V. Alao, the 1.2 Meg values you are using to set the DC bias seams rather high to me.
Also, as shown the Dc bias point of the net to the left of C19 is floating when none of the switches are closed. That will result in a pop when the switches turn on and off. That net should also be biased at the same DC level as the opamps are. And, asuming that your Audio_out is ground referenced, the polarity of C19 should be reversed, since the left side of that cap should be at +2.5V