me too, exact same situation. 3 weeks of cool printing and then heatbed stopped getting up to temp after a 3 day PETG high temp print. My cord looks fine though and I do not want to take it off and look as I am sure that will disqualify warranty. Unfortunately, they are all on CNY and there is no support right now!
I am considering getting another printer from a different supplier until this gets fixed by SM team.