a98 displays white screen when p90 auto is pushed

[Smokey73]

I had an interesting "glitch" when using my a98 MFD this weekend.

a98 was functioning perfectly showing boat position with the Navionics chart with the P90 pilot head in standby, manually steering. Most of the time when I pressed the auto to lock heading, things worked perfectly. However, occasionally, when I went from standby to auto/locked heading the screen goes completely "white" with only the boat icon showing, no chart information at all. When I press the - + to change chart scale, the chart shows for a flash but the screen then goes white again with only the boat icon showing. If I wait a little longer and try it again it seems to work fine in Auto.

Any ideas about what is causing this?