Well isn’t this odd.

Pretty similar situation for me on Sunday.

Ran most of the morning quite normal, taking small draws every 10 to 15 minutes. Towards the end I swear I ran through 60 gallons of sap (2 hours) without getting a draw, kept blaming my draw off temp probe, moving it around, because it sure looked like syrup in the pan. Checked with a backup digital thermometer and both agreed. Was using far more defoamer than normal, but was keeping the foam in check.

Ran low on sap and quit firing, soon as the fire started to die the temp shot up, pulled off nearly a gallon.