Many iCloud-synced files show 0 KB and fail to download or restore on Mac

On March 28th, something went wrong: a large number of files on my MacBook that were synced with iCloud suddenly became 0 KB in size. These files are located in various folders, and when I try to download them again, nothing happens — they don’t recover. Unfortunately, I don’t have a Time Machine backup. These files are extremely important to me, and there are a lot of them.

Please advise on how I can recover these files.