I have never seen this behaviour before.
Check the secondary Firewall and make sure that the "Respond to ICMP echo and timestamp" setting has been correctly inherited from the primary's configuration.
When you run these tests is the PC on the same physical network as the interface you are trying to ping?
If not then try this first. This will help to isolate whether the problem is linked to the ICMP traffic not arriving or if it is something different.
A tcpdump could help as you will be able to see if the ICMP echo traffic is arriving in the first place and if there is then a corresponding ICMP echo response to prove that the Firewall is recognising and responding to the ping request.
Could it be that the switches connecting the two Firewalls is somehow blocking/filtering traffic to these 4 interfaces?
Trying swapping the cables over and see if the ping problem on these 4 interfaces moves from the secondary Firewall to the primary one. If it does, then I'd suggest that the switch is causing the problem, not the Firewalls.
Otherwise, given the odd nature of this behaviour, I would recommend that you raise a support request with McAfee technical support.