On both platforms (Android and iOS) the embedded browsers cache is being deleted every time the user shuts down the application (or the app is killed by the system, typically because the system needs to free some resources, this is happening “in the background” without letting the user know). This does not have anything to do with Locking of the app/database (Sticky runs in the background when the user just Locks it = it keeps/stores the browsers cache data also). So in other words - the cache is kept/stored only during ONE SESSION.
And finally - no, its not possible to delete the cache data manually. Instead - should it be required - shut down the application.