Gateway Monitoring not working

[sotirone]

Since I switched to my Fiber ISP, I have not been able to get the Gateway monitoring working.

I had it disabled up until now, but I plan on adding a 4G failover so I need to get it working.

My pfSense is behind the fiber modem/router in a DMZ and everything works properly.

Gateway monitoring works perfectly on my OpenVPN gateways and ping works perfectly through the WAN interface.

I have tried messing with the advanced settings to no avail.

Edit: I am trying with dpinger from the console:

dpinger -f -d 1 -B *PIA local VPN IP* 9.9.9.9

succeeds

while

dpinger -f -d 1 -B *WAN interface IP* 9.9.9.9

shows 0 0 100

Edit 2: I connected a second device to the ISP modem/router, dpinger fails to ping the modem/router and the second device when ping has no problem.
Also, dpinger fails to ping any external address when I bind it to the LAN interface and can only ping LAN IPs.
Binding it to localhost, I cannot ping external addresses while when I try to ping LAN addresses, I get sendto error: 49.
I am trying all of the above with data lengths > 0.