Application Ruleset Changing "by itself"!?

I have setup FW custom ruleset for an application.

Everything worked fine, until one day when I discovered that an extra rule “Allow All” had been added on top “by itself”.
That made my custom ruleset not blocking properly.

How could that have happened? How could a rule have been added “by itself”?

Did you ever set the firewall to ‘training mode’? Then that could be issue or if you have ‘create rules for safe applications’ enabled under firewall advanced settings.

I had it set to training mode a few years ago, but not since I created the ruleset in question.
‘Create rules for safe applications’ is not enabled.