There's a lot of variability - people will wire up a PBC with solderless cables and one or two connections won't work. I don't know why this is - the jacks are made by Neutrik, so they should be good, and we've been using Neutrik in products for 12 years. But, in the past year or so, this issue has popped up a few times with the particular model of jack we use in the PBC/10. Please try a different cable to see what happens.
One customer solved the problem by adding a small rubber ring to the plug's shaft, one that's just big enough to fit, and it keeps the plug from going in all the way. Just keeping the plug out an additional millimeter or so seems to be enough to get it to make contact properly. I've never tried this myself, but the customer says it works fine.