The elevator can change a parameter by itself if it gets a surge (often through the old phone line on the REM).
If you have 2 rs boards programmed the same it causes parity errors, can happen on lifts with 2 cop panels in the cabin.
But I think you should measure the voltage on the data of the rsl before and after disconnecting the button board (needs to be 0.32v). I think you probably actually have another hall button board dragging down the rsl line. It's only 9 floors so you could disconnect them all and reconnect them one by one if you have to.
I'm certain the Swedish supplier is not using Chinese boards.
