It is more likely that the RX560 is not fully backward compatible with your old motherboard.
The motherboard is PCIe x16 2.0, and your RX560 is PCIe x16 3.0 (and is claiming backward compatibility).
There was no way for the DP35DP to predict the future.
So, contact the manufacturer of the RX560 and ask them why it does not work. Perhaps they have a firmware update for the card (which I doubt).
Or, find a card that is truly backward compatible.
Or, get a new board. Even if you do find a card that is backward compatible, you will always be running in a degraded mode.
A nice, new, shiney graphics card deserves a nice new board.