Though I recently updated my machine to 26.1, I was seeing this odd behavior on 25.x as well.
I just added another internet connection to my firewall (had xfinity and just added Quantum). I setup multi-wan and I'm using 8.8.8.8 as the monitor IP on my xfinity connection. I setup the quantum connection to use 1.1.1.1 (and I've tried others). The setup all appears to be correct (`netstat -rn` looks correct). However, the problem I'm having is that the web interface is showing that the quantum connection latencies are insane, between 500 and 1200ms. However, if I ssh to the firewall and just `ping 1.1.1.1` from the command-line, I see what I would expect in no packet loss and a latency of 3 to 5ms.
I'm not sure how opnsense is testing these connections, exactly, but it appears there is a flaw in the evaluation or I'm missing some setting somewhere. I'm wondering if anyone else has run into this?