How to recover lost files from iCloud synchronization on Mac?

iCloud has just remove very important files from my computer.

For a day, I was basically unable to open and work on my project. iCloud had spent the entire day synchronizing from my computer to the cloud. During that time, no files were "present" on my disk.

I had let my mac synchronize overnight, to come back the next day with most of the important files in my project having disappeared.

This is unacceptable, and makes me want to throw my computer away and never touch an apple device again. If this project had an important deadline and/or I needed to present something, I guarantee this could have cost me that opportunity.

Has this happened to anyone before? If so, what did you do to fix it?

[Re-Titled by Moderator]

Original Title: Complaint about apple iCloud