So you should first run "killall pd" (and even killall -9 pd when it's stuck), before running you command.

Thanks! You are correct that a pd process with the netreceive is still running.
(fun fact, for me at least: When running it from a new terminal, the new netsend started printing on the previous terminal)

Now I tried it on a different mac. I was on macOS 10.9, now on 10.11.6 (same pd)

On first run, connection is established and patch works as expected, which is puzzling.

On second run (after effectively running killall pd, or killall -9 pd):

connecting stream socket: Connection refused (61)