For context, the phone/tablet Roon storage size keeps growing, thereby filling local storage and backup storage (unless backup is deactivated manually), presumably due to cache. (On my iPad, it currently uses 7.1 GB and on the iPhone 5.2 GB).
iOS provides no option to delete an app’s cache, so resetting/uninstalling the app is the only option, which is inconvenient as it requires reinstall and redoing the settings. It’s also completely non-obvious that this is occasionally necessary if it grew too far.
This is an old problem, e.g.,