Your problem has inspired an idea for a program that I may write:
The program would make GE follow a route
created from a navigation
program like SeaClear or OpenCPN
so that it would cache all the data so you could save it for later use.
As input the program would have:
1. The route(s) to follow. Created by a navigation
2. The normal scan height, say 20,000 feet.
3. The detailed height (for harbors, reefs
, etc. where you want more detail) say 5000 feet.
4. The speed to scan at. Adjustable while running so GE can download the data to be cached.
Normally the program would make GE scan at the normal height but when it detects two route
waypoints that are less than say 1/2 mile apart it would zoom in to the detail height then go back to the normal height.
Now it may not eliminate the problem you encountered, which I have no idea why it happened, but if it did, you could just rerun it.
Think its worth writing?