You can un-subscribe from the Agent Disabled Scorecard. With no subscription, you won't get the email. However, we do consider disabling agent to be a critical event, so the healthStatusChange scorecard will still be sent. Do you want AES to always ignore PEGA0010 alerts from your DEV system that have text indicating that the agent has been manually disabled? There is decision table included to allow custom criteria for when to ignore alerts - see decision table CustCheckIgnoreAlert.
In the scorecard subscription maintenance screen, the drop downs act as filters. You can see that there was no subscription for Agent failure scorecard specifically for cluster DevPegaPRPC7. You do not know if someone subscribed to Agent Failure scorecard for ALL clusters.
I suggest you clear the cluster filter -- change the drop down to 'Select ...'. That will show you subscriptions for all clusters - including subscriptions for ALL clusters.
The UI defaults the cluster filter to match the current cluster that one has been working with for dashboard and reporting.