were your pressure / time / temperature the same as you had done in the past?
One possibility is you glued up in high humidity, and humidity has since dropped. The panels would shrink widthwise, starting at the ends, so you'd get differential shrinkage along the glue line with gaps starting at each end.
I'm assuming the gap wasn't there during a dry fit - if not, the wood has moved and humidity change is the obvious culprit.
Another suggestion, new or old Cascamite? If it's got a Polyvine label on its old, they changed the formula, it failed, I stopped using it, now marketed by Ureka and back to its expected performance.