Missing Files After iCloud Storage Upgrade (Reliability/security issue of Apple iCloud service)

After upgrading my iCloud storage, my files started disappearing without my knowledge. At first, I noticed that some of my music files disappeared and my music library changed without any action on my part. Now, I cannot find several Numbers files that were stored in iCloud. I was using these files as of yesterday morning, but they are gone today.

I checked the iCloud Restore site, but there was nothing available to recover. I’m very concerned about the reliability of iCloud, as this has never happened with other cloud services.

I would like to know why this is happening, how I can recover my disappeared files, and what I can do to prevent this from happening again in the future.

Your prompt assistance would be greatly appreciated.