Files not synced between iMac and MacBook

Try going to iCloud.com using a computer browser to see if the items are there and whether they are from the iMac or the MacBook. That should show which computer isn't syncing. On the computer that isn't syncing, try going to System Preferences/iCloud (Apple ID if you are using Catalina) and stop syncing. Wait a couple of minutes, then recheck syncing. Allow time for the data to sync.

I have had this problem, too, but most often (I think) in reverse: I open files stored on the iCloud drive, work on them on my laptop, and then save them on the iCloud drive again. On the laptop, the iCloud Finder window shows the modified file with the correct date and time. But when I go to the iMac, the iCloud Finder windows shows the file with an older date and time.

I have lost work on account of this. I sometimes receive a warning about different versions of the file existing when I open it, but not always. It has me so spooked that I won't open a file if the Finder window shows the wrong date and time.

How to fix: One time I was able to get the iMac to recognize the updated file by completely shutting the iMac down and restarting. However, I tried that this morning and it didn't work. It does sometimes take time for the computer to check with the iCloud drive and update changes. However, I believe I gave the computer plenty of time this morning to do that and it didn't happen.

I called Apple support. They ultimately had me shut the iMac down and do the command-option-P-R start up sequence (hold the keys until the computer starts up, shuts down, and restarts). Afterwards, the iCloud Finder window still showed the wrong date and time for a few minutes, but then refreshed to show the correct date and time. Problem fixed, eh? At least this time.

The problem may be partly related to having the iMac in sleep mode when saving the modified file on the laptop. We did a test where I opened the file, modified it and saved it, all on the laptop while the iMac was awake, and the change showed up almost instantly on the iMac. Of course, that was after we'd zapped the PRAM, so who knows if that's a general solution.

Before doing any of this today, I did visit the iCloud via Safari, and the file stored on the iCloud did have the correct date and time, so I knew the laptop was properly saving the modified file to the iCloud. I knew the issue was getting the iMac to recognize that the iCloud version had been changed and to reflect those changes in the Finder.

So: restart, give the other computer some time, and if that doesn't work, try command-option-P-R.

Update: I had the problem again this morning and found a new work-around.

The file was last saved in iCloud (technically, inside a nested iCloud folder) last night at about 8 pm from my MacBook Air. The version that showed up on my iMac iCloud folder was from 2 pm yesterday, the previous version.

With the Finder, I tried to move the file from its nested iCloud folder to the top level of the iCloud. The file appeared in the Finder window for the iCloud, and I got that partially-filled in circle that's one form of a progress bar. It took a few seconds for the circle to go from all white to fully dark, indicating that the process of copying something had completed. But then the file that I had supposedly just moved to the top level of the iCloud vanished. When I went back to the nested folder where the file had been, it was there, but now it had the correct (8 pm) modified date and time.

Attempting to "move" the file from one "location" to another on the iCloud drive apparently prompted the OS to sync the iCloud window on the iMac with the actual iCloud drive. The old file I was attempting to move was erased, because it no longer existed on the iCloud drive, and the modified file was freshly downloaded from the iCloud to my iMac.

Faster and more convenient that doing the command-option-P-R restart.