Turn off iCloud sync on all your devices, delete the iCloud Stage Traxx 3 database by opening for example iPad Settings, tapping on your name on top, select iCloud and then manage storage. Here you can delete Stage Traxx 3.
On iPad/iPhone reinstall the app, restore your purchase and then load the last backup you made.
On Mac, delete the app, then delete the folder ~/Library/Containers/Stage Traxx 3. Then reinstall the app, restore your purchase and load the last backup.