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.
It is most likly the wood drying out on the ends faster than the rest. I had it happen once and it was simply shrinkage happening too fast. Now when I cut timber I usually leave it a couple of days before machining to size and gluing. Released tensions after sawing can cause twisting and unexpected shrinkage.
You sound are experienced in woodworking so unlikly you but did you test the moisture with a meter?Timber was purchased last month been sat in the shop
2 weeks ago I cut them
Machined them 10 days ago
Glue up 5” either end over length.
3 days in sash clamps
I then cut them down after all this they opened up in the ends