PSA -- uPnP/nat/pmp problems can be caused by network switches "IGMP Snooping"
Unless you have a good reason to have "IGNMP Snooping" on, then disable it on your network switches and any other devices.
uPnP broken on my network months ago and I never really worried about it too much except some games have problems with two instances running on the internal net. After spending a couple days troubleshooting, I narrowed it down to some of my network switches had "IGMP Snooping" enabled. As soon as I disabled that, uPnP/NAT/PMP started working.
I learned a lot about miniupnpd in the process, and learned even more about capturing network traffic and wireshark, and about the various protocols involved.
What made it more frustrating to troubleshoot, is that it was working on any of the several rasp pi's I have on my net, but any of the windows 10 boxes upnp was broken.
It turns out that IGMP Snooping was enabled on the switches that sit between my firewall and the windows 10 boxes (by coincidence, not by design).
After sorting this out, the miniupnp client (upnpc-static.exe) sees the pfsense firewall as an IGD, and I cna use the client to add/remove mappings as expected.
I would agree that understanding what is configured and how it works and functions is yeah a big plus in knowing if you should enable whatever or not, and or if you need it or not, etc. ;)