This is really a very strange problem. By swapping them, you have proven that it must be an
issue somewhere in the router or network settings somewhere. I would have also suspected a
wiring problem, but it works within the LAN which means this is not the issue.
If I had a TM-V71A, I would try it out from here, but I don't. I am not sure what to do next,
except maybe a completely different number sequence, like 15000-15002 or similar.
I could take a look at both your settings and router if you want, but somehow I doubt that I will
find something.
Also make sure that SIP ALG is turned off in your router. I would assume that the TS-480 would also not
have worked with it on, but I have seen weirder things. SIP ALG turned on and even router firewalls have
caused these types of problems before. This goes for both sides, not only the radio.
Good luck and keep us informed. If you want me to look anyway, just let me know.
73,
Mitch DJ0QN / K7DX