Are you using the old style hotend? From the sound of it it seems to be the classic heat creep issue addressed in Findings and solution for the Snapmaker J1 clogging problem.
Where after a long print the heat will eventually creep into the cold side of the heatbreak causing the plastic to melt in the heatbreak. The print will continue fine for a while until the feed rate suddenly increase to the point where the incoming heat is no longer enough to melt the plastic or after the print stops and forms a plug.
This normally should not happen as the heatsink and fan should keep the cold side cold but the old style hotend is known to often have severe underapplication of thermal compound from factory. There are a couple of solutions to this in the abovementioned thread but you can also check out: