Apologies for the delay, had to wrestle my multimeter back from Son #1, who is building some kind of weird Midi switcher for his Strymon delay, using a Teensie board.
Here's the circuit diagram. My understanding is that R1 is the pulldown resistor for the input cap C1, and R6 is the pulldown resistor for the output cap C4.
One side of C1 is connected to ground, the other side gives open circuit. The -ve side of C4 is connected to ground through R6, it's showing IM on the highest setting of my meter which is the value of R6. If that all checks out, what should I look at next? I think a check of C4 is in order, but I have to start unsoldering pots to get at the connections for C4.