I have a Boss FS-5L footswitch I use with my Roland Cube, I've had it for a couple years now. Recently it's started requiring two stomps to switch channels and I haven't got a clue why. Like I hit it once and the light goes on but the channel doesn't switch, then I hit it again and the light goes off and it finally switches. I've tried different cables and new batteries but it still does it. It makes live playing a little tricky when I have to double stomp. Thoughts?
Isolate the problem.

First the amp. At the footswitch end of the cable just use a paper clip to short the center tip to the outer ring of the connector. This should trigger the channels to change.

Then test the footswitch. Probe the output with a multimeter and verify if hitting the switch toggles the output resistance from very high to very low value.