Stuck with what's happening with MQTT topics

It isn't to do with one's IP it is only specific IPs that give the problem. When one publishes "58.169.129.172" to a topic (any topic) mqttexplorer shows {}. I think a clue is that if you click on the value and look in the right hand side it says Decoded SparkplugB

See MQTT-Explorer 0.4.0-beta4 SparkplugB decode some strings as "{}" · Issue #792 · thomasnordquist/MQTT-Explorer · GitHub

It is fixed in the edge version which you can get by running
sudo snap refresh --edge mqtt-explorer