External join server issue (loracloud.com)

Hello!
I was successfully using an external join server for my nodes to join for a while, but previous week my setup just stopped working after I power-cycled my node. The server does not send join-accept anymore. This is how the live data tab looks for one of my nodes:
image
Unfortunately, the error messages are not helpful for me as I cannot find any detailed description.
Can anybody give me a hint?

P.S. Just to make sure we are on the same page - there have not been any configuration changes in my TTN v3 console, nor in the node or join server.