My footswitch stopped responding under the following scenario.
Marshall Code 50
Four button footswitch
Macbook pro connected via USB
Sound output set to Marshall Code
Playing Youtube videos through the amp and playing along
After a while, the footswitch stopped responding. I couldn't change banks or position within a bank.
Unplugging the USB cable seemed to get things going but footswitch stopped responding again shortly after.
Turning the amp off an on again resolved the issue.