If you use Touch ID and you do any of the following:
- replace your device,
- change a safe name,
- change a safe location (local vs iCloud),
- update Touch ID (by adding a face/fingerprint),
- reset Touch ID.
The saved password will be lost - so before you do this make sure you remember your safe password.
If you have forgotten your safe password, you can change the password while Touch ID is still working.