The http 401 refusal is probably due to an outdated version of the TVDB scraper add-on; the API keys used by Kodi in the add-on were revoked recently due to widespread copying/abuse from pirate add-ons. You need to update the scraper so it uses an updated/valid key.
If the box is not showing add-ons at all try add-on a 10-second "wait for network" boot delay in LibreELEC settings or context click on the Kodi repo and run 'check for updates' to see what it finds.
This solved my issue - manual checking updates for the Kodi repository.
Thanks!