[CA] No Navigation Data message

[DO335]

Hi Chuck,
I got back to my boat and changed the network so it is much simpler and only has Raymarine units attached, see diagram file attached. I have only the 3 ST70 instruments, the p70, the ACU400 and EV2 attached to the network now, no MFD, no third party units. All of the ST70 instruments (Speed, Depth, Wind) are operating correctly. Even with this set up when I push the auto button the rudder slowly turns to one side and I'm still seeing the "No Navigation Data message on the p70. These units all worked before and I haven't changed any software on any of them since they last worked correctly. Is it possible the p70 has failed or is it something else? Maybe a bad cable?
Thanks,
Steve