I am having this exact issue on TWO brand new printers. One last week and another just today. There is definitely a bad batch of parts going around! I will check into your solution!
I had this exact same issue. I just received this machine last week and had some awesome first prints, then spaghetti. I set my hot end temp to 240 and that fixed it (after banging my head on the table, then finding this post, then trying your fix). I already ordered new heater/thermistor parts, but I’ll still contact Bambu about it. Thanks for the help!