Update:

I was just doing some more work on my Ibanez TS808 pedal and I think I have finally cracked it this time round, in the schematic I posted, there is a small value capacitor (1000pf) going from one end of a 22 Ohm resistor to circuit ground, in my pedal it is a 10,000pF (10nF) ceramic capacitor, which appears to be the cause of the footswitching issue I've been experiencing, what I believe is going on with the capacitor is that it has gone leaky, but to detect it I had to set my digital multimeter to it's highest resistance range, I compared it with another known good 10nF cap (a yellow polypropylene type) and got very different results, so I tried using the yellow 10nF cap as a replacement, and now the pedal seems to reliably footswitching again like it's supposed to, I'll give it some soak-testing for some time just to be sure that I have finally fixed it for good now.