Hello, I'm currently experiencing similar issue. My WAN keeps dropping every few days. I couldn't figure it out until I read the gateway log that seems to suggest the WAN interface is the issue. Comcast is my ISP, and I own my own cable modem (Netgear CM700). My gateway {pfSense 2.5.2} is an old repurposed HP workstation with a 4-port intel NIC. I have been running pfSense for about two years. I have a fairly complex system with multiple LANs /VLans and a plethora of managed switches. It could be my cable modem that's on its last leg since it has a poor reputation (the controversial PUMA chipset) or my switches due to an improperly configured STP because sometimes the issue would be temporarily resolved after rebooting only the switches. However, the issue continues after properly configuring STP. Refreshing openvpn would also temporarily resolved the issue. Also quickly unplugging and plugging solely the WAN ethernet cable would temporarily resolved the problem. I'm currently at a lost for solutions. It wasn't until today when I finally really read the pfSense logs in details that pointed me to the potential culprit, the WAN interface. Before that, I tried all types of fruitless solutions. I serendipitously stumbled on your potential solution, changing the speed/duplex of the WAN interface from autoselect to 1000 base T full duplex. I have applied it and hope that it works; fingers crossed and will find out in a few days if this was the issue.