That’s a good first clue.
- Do you have any other sync tools activated? Obsidian Sync? If so, that is risky, and can cause issues. Only use one.
- Are you on Windows? From the Obsidian help, “iCloud can be used to sync vaults between iOS and macOS. However, iCloud Drive on Windows may lead to file duplication or corruption.” This might be the reason.
- Do you have iCloud set to have the files always downloaded? (That’s important.)
- How many devices, and what devices are you syncing to? (But point number 2 is more important.)