I'm very sorry you had this technical problem, I would like to help. I can confirm the files aren't corrupt considering no other testers or buyers reported this issue, which is why I asked you to try a different file manager before any other solution.
And we do already suggest using a third-party extraction tool. If you look at the download page, the included video for Android users recommends Files by Google (https://play.google.com/store/apps/details?id=com.google.android.apps.nbu.files).