I have noticed they don't spawn anymore on map creation. Depending on your chosen frequency there would be an initial spawn, and then they would replenish based on the frequency. Now there is no initial spawn, on map creation there is none, and it solely rely on the slow replenishing aspect. Maybe its a balance so prevent you or the ai getting a huge bonus at the start from the mass of anomalies.
Edit: My mistake, maybe it was fixed or i was just wrong. There is in fact a initial spawn on map creation. Just tested and there were lots.
