Scheduling background activities like making backups has moved from cron to launchd, and now to a more complex system. This has reduced the reliability of macOS and made it harder to support.
Background activities scheduled by third-party software currently use launchd, and run the risk of affecting the user. Would GCD be a better choice of dispatcher?
Schedule a periodic task as a Launch Agent. How close to the expected time does macOS actually run it?
Does macOS scheduling fail when it has been running for more than 10 days? Irregular backups suggest that it does.
If the kernel is the heart of OS X, launchd is its brain. Use it to run periodic tasks such as synchronising folders automatically.
Macs are increasingly reliant on background services, and increasingly vulnerable to their problems. Mastering the services on your Mac will help make it faster and more stable.