Using two MM instances and two EDLs for the same IP lists adds overhead to the firewall and could hit the EDL IP number limit for your hardware.
If an EDL source URL is unreachable, PAN OS just keeps using the old EDL values, so I would not be overly concerned if you can endure it 24-48 hours.
I would rather like to be warned when MM goes down, so I suggest configuring something like Nagios to ping and check https.
And I would like to be notified if a Miner fails updating a list N times: right now it seems the alert is only shown in the web UI.
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