System Protection (whether under Windows 7, 8.1, or 10) is NOT a backup and recovery utility in any meaningful sense. And it has a long history, as Glenn has indicated, of being flaky, at best, for what it's supposed to be good for - rolling back a recent change like the installation of a single program.
It is not even in the same class as a true backup and recovery suite. I keep it turned on for the sake of convenience so if I need to do a very simple rollback I can try it, but I long ago learned that one should never count on System Protection being a robust system that works each and every time, or even close to it.
That's one of the reasons, among many, that taking full system images and separate user data backups is essential. And if the data is really, really critical, either taking multiple backups or immediately copying off the latest local one to remote storage, away from the source material, so it's available in the event of fire, flood, or other natural disaster. That may be overkill for most home users, but even some of them do this to have as much insurance in the event of a need for recovery as they can get.
Brian - Windows 10 Pro, 64-Bit, Version 1909, Build 18363
The purpose of education is not to validate ignorance but to overcome it.