seeing this thread, I have a similar issue. Here is a video of the behavior.
Tapping hard on the keys makes normal sounds.
preset of electric piano sounds ok. The video is on stage piano (001). factory reset didnt help
https://drive.google.com/file/d/1G4iyfJThXEGN2cskpIuK64J_yx5LCtzO/view?usp=sharing