What is causing my Pages documents to disappear?

No Apple employees participate in these public, user-supported communities. I have never lost a Pages document on iCloud on any version of iOS or iPadOS, so application unreliability or faults do not enter the equation in my experience. Lost document prevention is shouldered by the individual user, and why yours are disappearing when mine don't has no explanation.

Apple's iCloud does have a 30-day sliding window for document restoration.

Recover deleted files on iCloud.com - Apple Support

Beyond that, you can send feedback directly to the Pages product team from within the application.

What device is this problem occurring on?

This article should help you

Delete or recover a document in Pages for iCloud - Apple Support

There’s is a chance that the pages are crashing, so try rebooting your device.

good luck

I use Pages on an almost daily basis, and have never lost any. Perhaps you are saving the to a different location than the one you are looking in.

And where has it been brought anyone’s attention? I have never seen any reports of it in this iPhone forum that I have been following for almost 18 years.