I had a problem with losing the heading data from my SCX-20 satellite compass when I started the engines. I would have to reboot all the electronics after which it all worked fine again. What was surprising is that while it was clear that a temporary voltage drop from the heavy load of starting the Diesel engines was causing the SCX-20 to drop out, none of the other electronics seemed to be affected.
As Johnny suggested, focus on the power supply for your NMEA 2000 network. In my case, the SCX-20 was the at the end of a long cable run mounted up on the tower sunshade over 20 feet from the helm. I installed a second power tap closer to the SCX-20 to reduce the voltage drop, which solved the problem. The root cause of the issue was that my engine starting batteries were starting to go bad and the combiner was engaging and thus the house bank was "helping" start the engines, which dropped the voltage to the electronics.
The surprising part to me was that the network "lost" the SCX-20 permanent once it dropped off even though it quickly restarted and was sending out data. That makes no sense and is different from how other devices behave, For example, if I turn off my AIS transponder, which is a NMEA 2000 device, the AIS data will reappear once it comes back on without the necessity of rebooting the MFD displays.