Since it has a pot to adjust the gain, your board seems came with lower gain, resulting in higher real temps than requested.
I think I'm goign to set the default calibration values much lower by default, to avoid more issues like these.
It's better to get 100ºC at Cal250 step, than 300.
Please try the attached FW. After flashing, make a full reset by pressing the button before turning on the station.
Then go into Calibration / Adjust and set a rough aproximation there.
Save and run Calibration / Start.
And yes, the AliExpress temp probes are absolutely crap.
The one that came with my Uni-T DMM did really well.
I lost it, the others have given a lot of headaches.
Touch, you get 400°C. Remove and touch again, you get 370.
Clean everything , new solder, touch again, 385.
To make it worse, my probes came with the last 5mm twisted.
That's ok when you put the whole thing inside a hot oven, but when you measure a small spot, it will short out the voltage and read something on the middle. I got 150°C less!
After de-twisting it got better. But it's extremely sensitive to contamination.
Ex. The tiniest burned flux will stick to it causing lower readings. I have to scrape the small metal ball, ensure it's clean and shiny, place it under the cold tip ensuring that it makes enough force, heat the tip until it melts solder and play a bit with the position. After that I can crank the temps up.
But if the probe comes out at 450°C, putting it back will read 20-40°C less, requiring another exhaustive cleaning. Crap.
I think the probe wires are too thick, stealing heat from the tip of the probe, so any dirt will cause some isolation and wrong readings.