Update:

decided to try the muff again one last time last night before sending it back to EHX and suddenly its working perfectly again.
This perplexed me so I checked again for loose wires and found none.
I’m guessing that something must have been lying across two of the connections shorting it out that was dislodged when I opened it.

But anyways its working so happy days

Cool might try that, now to find the receipt.
but any suggestions in case I cant.