If your files look broken or blank when you open them after you update the Documents app, first of all, please try rebooting your iPhone or iPad.
When your audio or video file is shown as broken, please make sure this file is fully downloaded - you may also try opening this file in any other app to make sure the problem is not file specific.
In case the files in your iCloud folder look broken, please make sure that you have enough free space on your device (you can check this in iOS Settings of your device > General) as well as your iCloud account (for this, go to iOS Settings > Apple ID, iCloud, Media & Purchases > iCloud); in the meantime, you can access files in the Files app > iCloud Drive > Documents folder.
If it doesn't help, please send us logs - we're happy to help you personally:
- Open Documents.
- Go to Settings > Support > toggle on Detailed logging.
- Reproduce the issue if possible or let the app run for some time.
- Go to Settings > Support > Send Feedback.