The Mapbox SDK keeps a cache of map data, for fast loading. Any delay you see in loading will more likely be due to iOS’s memory restrictions.

If iOS wants more memory for other apps, it sends a memory warning out to all apps currently running. When Arc receives that memory warning it is required to remove as much stuff from memory as possible. Sometimes that means Arc has to remove the map, because there is nothing else left to be removed.

So when you see the map area empty, then the map appear some seconds later, that is because iOS has demanded that Arc free up some memory, and the map was the last remaining thing that Arc could discard. Arc then has to reload the map, once the app enters the foreground. (You can sometimes also see this happen even when the app is already in the foreground, if iOS is being particularly demanding of memory).

When the map is loading, it will almost always be loading to show a map region that has already been cached in Mapbox’s database. So the loading time isn’t due to network requests, but instead is simply due to the CPU / GPU effort required for building the initial map view.