I recently ran into that issue as well and PRed a fix for that: connman: ignore kernel-managed netdev and improve resolv.conf handling by HiassofT · Pull Request #3883 · LibreELEC/LibreELEC.tv · GitHub
This fix is included in Milhouse nightly builds since #1002 and should make it's way into the next LibreELEC release if testing goes fine.
LibreELEC Testbuilds for x86_64 (Kodi 19.0)
LibreELEC Testbuilds for RaspberryPi (Kodi 19.0)
Some feedback / test results would be highly appreciated.
so long,
Hias