I did not update the firmware since the Ultimaker 3 was purchased in 2019. C The firmware I believe is UM3: 4.3.3.20180529. Should I update it? The PLA has not been dried in a while. I will do this today and try to print again. The print core 1 is 0.4 mm. I did a print core cleaning hot and cold pull. When I change the filament, it flows nicely out of the print core until I stop it. I also tried to print with a new print core 2 (0.4 mm), (never used) and the behavior is the same, e.g. a perfect first layer with good adhesion to the glass plate, but printer stops extruding while still pretending to print.
I set the temperature at 200C and 60 mm/s print speed. I tried to make some observations when it stopped printing the first layer. When I start to print, the set temperature is at 205/205C, when my problem of extruding stops at the first layer the set temperature is at 198/200C. As it continues the printing motion without extrusion, the set temperature is at 199/200C. The fan in the front is turning.