We do not pre-compute most of our data, you are the computer! We only generate the data that is really viewed by you. When a part of the world is viewed for the first time, we generate the data for the map at the time of request. In some cases this will cause a slower response. However, thanks to your request the data is generated and cached on our server and immediately available when you or someone else visits this place again.
Sometimes when you switch from a mobile network to WiFi or vice versa, OpenScienceMap can have problems to get the data from our server. In this case just restart OpenScienceMap!