@dikman @Constabulary So I've tried to reset to factory settings, without any luck — because the machine still didn't work correctly. When I reset to factory settings, the display shows "OK", meaning the reset was successfully done.
I wonder if it might have anything to do with the speed governor? It just seems very strange to me...
Here's the manual: http://en.chinajack.com/DownLoad/201706271100232.pdf
The manual is not exactly made for the same model, it seems (not sure tho).
Image of E5-error
Link to a demonstration video