Have you looked at Ashley's tutorial here ?
Saving can take a moment to complete, and the game keeps running in the mean time. Once saving has completed, the System trigger On save complete triggers.
Similarly loading can take a moment to finish, and triggers On load complete when done. Note any changes made after the Save action, but before On save complete triggers, may still be saved.
If you try to load from a slot that hasn't been saved to yet, On load failed will trigger.
Are you checking 'On save complete' ?