V3 Switching Board -- IC1/Relay trouble

[Chrisx5x5]

Built a Merman using the V3 switching board and here's the problem with the relay/control IC:
IC 1 shows 5V at pin 1, 5V at pin 7 when in effect mode and 0V when in bypass mode, all of which is correct.
When I connect power I can hear the relay click, putting it into bypass mode.
Then if I depress the footswitch once, I hear the click, the LED lights and the pedal goes into effect mode just as it should.  It works just fine.
But then closing the footswitch again has no effect: the relay doesn't cycle, the pedal doesn't go into bypass, no discernible voltage at pins 3 and 6 (which trigger the relay).
Does that sound like it could be anything but a fault in IC1?  I haven't reflowed the solder joints but the behavior suggests that the IC is having no problem communicating with the relay or the footswitch.  I can try desoldering and replacing it with another control chip I have, but before going that route I'd like to know if there's anything obvious that I'm missing.
Any suggestions very much appreciated.