I suppose that I have to agree with the fallibility of the iCloud drive. I keep files (Excel spreadsheets) in my iCoud drive to access from my multiple machines. During the old sync folder days, I never experienced a problem with losing sync on hundreds of files. I started using the iCloud drive to wean myself off of JustCloud (pay for use), and WHAM ... i lost sync on one of my files. I was given the choice of which file to use, and I selected. All seemed to be working until the next attempt (today). Now I have a choice of one file, and when I select it, it will not open. I can double click to see that the contents are there, but I have no way to access it. I cannot even drag it to a local folder location. I get a conflict message, and it refuses to allow me to do anything with it. Fortunately, I can copy/paste to a folder without prevention.
Just a comment on how it does not perform as flawlessly as some may think.