I tried downloading all my videos into the [redacted] app. But then I ended up redownloading them back into my photo album. ever since then, I had the problem. So, what do I do?
If you were only copying the videos into the app then they should work like they did before. If you moved the videos from the Photos app into the other app and then moved them back then it’s possible that more time is needed to make sure that everything is moved back. Login to iCloud dot com to see if the videos are present. (I’m assuming you have iCloud Photo Library enabled).