Power / lock button intermittently unresponsive

I have two friends with very similar issues. Both have iPhone 5s (5, not 5s) and both are complaining that their power buttons frequently don't respond to clicks. They've taken the iPhones out of their cases, tried restoring, power cycled the device, etc with no change in behavior.

I've taken a look at each and tactile feedback is still present, you can feel the click when you press the power button, but 25-50% of the time the button press doesn't register with the device.

Has anyone else experienced this? If I were to repair it for them would the likely part be the Audio Control & Power Button cable?