ENDIAN Firewall - DNS fails after about 1 hour

When Endian Firewall runs for about 1 hour suddenly DNS lookup fails from clients on the network.

I have no additional DNS-server installed on my LAN, I just use Endian as a DNS proxy.

But like I said, after about an hour I can no longer visite webpages. When initiating 'yum update' on a local client it clearly states 'failure in name resolution'.
This problem is not situated on just this local client as I have the same problem on all my LAN-clients.

CPU usage is 4%, Memory usage is 51%, swap usage 0%.

What could be causing this ?

Restarting the Endian firewall resolves the issue...

Using Endian Community release 2.2