CW. Depends. There were two versions of the app. I think the old one disappeared with iOS 8 or 9
edit. The app was updated. The new app version was incompatible. There is no way of getting the old version.
taking a big guess, the reset forced app updates (lesson, annoyingly, is never allow automatic app updates) which overwrote the existing app with the incompatible new one. The iPad was not backed up to iCloud which would have just set it back to what it was.
the reset may have been a complete start from scratch rather than a “reboot”