Same problem here. When in map view, zooming in does not reveal the areas around radar dishes. It's as if the radars are not there or not working. I've removed and replaced radar dishes to see if it made a difference.
Hmm, came back to the game after about 3 hours. Radar now works. But map has doubled in size, much more of the map is revealed, biters are back, all over... I had to go back to a save game from a couple of days ago. Bummer. Probably something with a mod I'm running.
Tested that everything is still working correctly. Must be some other mod you are using. If you could post your mod list I might be able to find out whats going on.
Try leaving the map running for several minutes. It takes a while for Factorio to regenerate parts of the map covered by radar and radars will not update until the generation is finished.
