Those are only your Kodi debug logs. However, to hazard a guess, it looks like your network is not properly being brought up, and that includes the loopback interface on 127.0.0.1. Unfortunately, without boot logs/dmesg, I'm not sure we can really be up much help here.
LibreELEC (and similarly, OpenELEC) are troublesome to work with and troubleshoot, because they are not full OSes, but merely a minimal embedded OS to run for a single purpose.
Also, what does the log for Tvheadend show when it starts up? Is it starting up, or is it erroring out? Perhaps the problem you can't connect is because Tvheadend is not running, not that there is a problem with your plugin. (The Kodi logs showed the plugin loading properly, just that it could not connect to the HTSP server running on 127.0.0.1:9982.)