SafariBookmarksSyncAgent preventing sleep

My High Sierra 10.13.3 Macbook Pro never sleeps.

Looking in Activity Monitor, SafariBookmarksSyncAgent seems to be the only thing with Preventing Sleep set to Yes.

If I kill it, it comes back, and launchctl doesn't seem able to stop it either.

Never had the problem before the HS upgrade.

I've never logged into iCloud on this Mac, and don't wish to do so.