Ionic 1 app no longer in Copy To menu

My ionic v1 app registers itself for a number of file extensions so that it becomes visible in the Share menu on iOS. Up until iOS 12 this worked beautifully, but after upgrading to iOS 13, my app icon is still shown in the Mail app, but when I tap the Share icon, my app is no longer listed as one of the apps that can open this type of file. I haven’t been able to find anything in the documentation solar that would explain this. But, since there are other apps that are still listed, it must be possible to get my app in there as well. Does anyone have an idea why this happened and a possible solution? My app really relies on this functionality to work.