SharePoint Rule Send an Email created by Former EE fail

SP Rules created by a former employee are no longer sent. The Rule was created to email other current users when a field was modified. The Rule was not set to email the former ee, but other users. The only thing that changed is the person who created the rule is no longer with our company.

Once the Rule was duplicated by a current user it started working again.

Rules are sent via <email address removed for privacy reasons> so why should it matter who created the rule?

I see this becoming a large problem as SharePoint Alerts retire and users are now using Rules. For business critical Rules, we've used a Service Account to create the rules to prevent failure in the future.

I can certainly understand rules that are created to go to former ee to no longer work since their account is no longer active, but if it's set up to go to other users that are still active, it should remain active and not fail regardless of the status of the created by.