PfSense locks up when using virtual IPs with NAT

xciter327

This is more of a PSA regarding something that has been bothering us since pfSense version 2.3.x at least.

Description of issue:
pfSense randomly locks up and stops working. Our first occurrence of this was in February this year.

Configuration Description:

Public IP range routed to the WAN(or CARP IP) of the pfsense device
Virtual IP configured for NAT with one of the following options: Proxy ARP or "Other subnet"
NAT rule configured to use the above IP
This happens in HA mode as well. First the primary unit freezes and shortly after, then backup unit starts freezing.
There is nothing allowed incoming on the WAN side. LAN side is allow all. There is a floating rule to block access to management ports from LAN side ports.

Observations:

Traffic levels don't seem to matter. We have experienced this with traffic levels between 100Mbps and 2000Mbps.
Absolutely no logs or crash reports are generated of the event.
Remote console / Directly connected screen is un-responsive
Happens with multiple hardware devices. We've tried 2 different Supermicro modules(same/similar as Netgate devices and 1 Dell Server)
Bought commercial support for one of the affected locations. Netgate suggeted we switch to "Other subnet" for NAT "Overload". Still crashes.
IP Alias or NAT-ing on the WAN address does not suffer the same issues. Seems to only happen when using a NAT "Pool".
I've not tried using a "Host alias" as a NAT overload network

All the servers involved have passed a 24 hour Memtest64.