Yamaha DGX-650 Keys do not play when a side by key is pressed

by Guido
(UK)

Hi everyone, this is first time I issue a query so I hope I am doing it right, and many thanks in advance for any tips.

I have a DGX-650 piano and from few weeks ago, it developed this problem, when a key is pressed the side by key will not play until the first key is released. This happens with key pairs only. I have reset the piano to factory settings, and did not help.

Please let me know if anyone has some suggestions. Is the piano damaged?, is there any way to repair this problem? has anyone had same problem?

Thank you very mcuh