I have the same issue on iOS. Deleting photos does not clear up storage space. I don't have a cloud storage plan, so there isn't an option to "Clear Cache". The Local Storage pane under settings indicates 5.03GB for locally stored copies and 0.00GB for cached files while the OS indicates that Lightroom is consuming 19.52GB of space. The only workaround I have found is to uninstall the App and reinstall it, but that isn't possible when working away from an Internet connection.