Cisco Firewall :: High CPU Utilization On ASA 5550?

I have Active Standby ASA5550 setup with VPN premium license. A few days back we had a requirement of SSL VPN connection for and we got a temporary from Cisco for same, this license expired and the ASA reverted to it's original license. 3 4 days after this we saw a sudden increase in CPU utilization (upto 90% + -5%) on the ASA during production hours but were not able to figure out the reason, in order to restore the services we failovered the firewall to secondary and everything worked fine. We were suspecting one of the following but there were no logs for any of this
 
1. The ASA hardware was haivng problem

2. Some client was doing a DoS attack to bring down the ASA (no logs for this as well).
 
We took a downtime to look further by failovering the ASA back to primary and it worked fine without any issues ruling out the 1st option. We also came across a licesing doc [URL]
  
Downgrading any license (for example, going from 10 contexts to 2 contexts).
 
# Note If  a temporary license expires, and the permanent license is a downgrade,  then you do not need to immediately reload the security appliance; the  next time you reload, the permanent license is restored.
  
As per this doc, sooner or later a restart was required on the ASA. We restarted secondary ASA and everthing was fine but when we restarted the primary ASA by swtiching over to secondary some of the server (not all) in the DMZ stopped working (even ICMP unreachable) and only came back to normal when the primary ASA was restored and working fine (with failover).
 
The reboot was done by shuting down the physical link between the Core switch and ASA inside individually.
 
I am not sure what could be the issue that the servers in the DMZ wen unreachable.