Sorry for the late reply.
I tried on a laptop, and I get the same ERR.

1) I added 127.0.0.*;, it made no difference 2) The nodes actually connect to the server's IP address. the URL with localhost is to test the same in the browser. I only programmed the nodes to give a visible error when connecting to the server fails, and this happens predictably when I shut down the ...

I experimented with API Protection and Trusted network, but it didn't help.

I have three sensor nodes, each of which pushes some sensor values to the JSON API. After I moved one of my sensor nodes around the house (something I do regularly with this particular node) all devices stopped working at the same time. Sensors are added like this: Screenshot from 2024-03-31 19-35 ...