I had this issue when setting up my server. I have it working now, and suspect it was to do with image caching issues. I manually went into the ServerGrid.json file and edited "lastImageOverride" keys (for each grid definition, and for the main file) and set them to something recent ("2018-12-27T21:57:24.4325931Z" in my case). The values aren't being set by the map editor it seems, and somehow bad images seemed to get cached for my WorldAtladID. I'm pretty sure, but not 100% that this was my issue. Once you've set those values, next time you log into the game, it should just magically have the new images (fingers crossed).
MAP is gray
in Dedicated Server and Developer Tools Discussion
Posted
I had this issue when setting up my server. I have it working now, and suspect it was to do with image caching issues. I manually went into the ServerGrid.json file and edited "lastImageOverride" keys (for each grid definition, and for the main file) and set them to something recent ("2018-12-27T21:57:24.4325931Z" in my case). The values aren't being set by the map editor it seems, and somehow bad images seemed to get cached for my WorldAtladID. I'm pretty sure, but not 100% that this was my issue. Once you've set those values, next time you log into the game, it should just magically have the new images (fingers crossed).