The default gateway target, which seems to be a DHCP server in my ISP
While I didn't wireshark it this time, I have done so in the past. What I saw was a bunch of dup packet responses getting sent from my WAN. WAN ingress was 100Mb/s and LAN egress was about 70Mb/s. PFSense seems to have filtered out the already acknowledged traffic and responded on behalf of my computer. When I did a trace route to these target IP addresses, while I was still downloading from them, I saw normal 2ms ping here, 10ms ping there, 20ms ping there, then right before it got to the seeder, 2,000+ ms pings. I samples about 10 TCP connections that were causing all of those dup packet responses, and they all had the same large ping jump 1-2 hops away from reaching them, but otherwise good hop pings within their ISP's network. Just not the last 2.
I do use HFSC and CoDel
My ISP does also have some unidentified AQM. All I know is without any shaping on my end, DSLReports says I get about 20-30ms of buffer bloat. With shaping on my end, I get bloat down to about 1ms. This is also reflected when I had a DOS volume attack tested against my connection. I had a service send 110Mb/s at my 100Mb connection and I saw about 10% loss and typically 30ms-40ms of latency. Even when pushed to 200Mb flood, still 30ms-40ms, but something like 50%+ loss. I forget exactly how much, but my connection was dead.