About 15 minutes into a print the plastic stops coming out of the extruder but the motors keep moving it as if it is still printing. I then pull the plastic out, check for clogs (of which I don't find any) then reload the plastic. It will again start printing but will stop after about 15 minutes. It used to print for hours without any problem. I tried replacing the nozzle in case it was clogged with particles and burned material but it is still having that problem.Printer: Flashforge Inventor 2Plastic: PLAThank you.