Thanks awiouy and nickr.

should be fine!?
When you say "LAN is not connected" - was lan connected when you booted, then you unplugged it, or was it disconnected at bootup?
What does netstat tell you about what IP addresses tvheadend is bound to? netstat -tanp|grep 9981
Tethering disabled, reboot, WLAN connect to my home network and gets IP 192.168.11.67 and with that I can access 192.168.11.67:9981
tcp 0 0 0.0.0.0:9981 0.0.0.0:* LISTEN 492/tvheadend
tcp 0 0 192.168.11.67:9981 192.168.4.1:59229 ESTABLISHED 492/tvheadend
Tethering enabled, reboot, WLAN gets IP 192.168.0.1 and I access it from 192.168.0.2, 192.168.0.1:9981 says "ERR_CONNECTION_REFUSED"
LibreELEC:~ # netstat -tanp
Active Internet connections (servers and established)
Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name
tcp 0 0 0.0.0.0:4713 0.0.0.0:* LISTEN 261/pulseaudio
tcp 0 0 0.0.0.0:5900 0.0.0.0:* LISTEN 517/dispmanx_vncser
tcp 0 0 0.0.0.0:111 0.0.0.0:* LISTEN 1/systemd
tcp 0 0 0.0.0.0:8080 0.0.0.0:* LISTEN 516/kodi.bin
tcp 0 0 0.0.0.0:1203 0.0.0.0:* LISTEN 516/kodi.bin
tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN 322/sshd
tcp 0 0 0.0.0.0:36666 0.0.0.0:* LISTEN 516/kodi.bin
tcp 0 1392 192.168.0.1:22 192.168.0.2:59703 ESTABLISHED 589/0
tcp 0 0 :::4713 :::* LISTEN 261/pulseaudio
tcp 0 0 :::5900 :::* LISTEN 517/dispmanx_vncser
tcp 0 0 :::111 :::* LISTEN 1/systemd
tcp 0 0 :::8080 :::* LISTEN 516/kodi.bin
tcp 0 0 :::22 :::* LISTEN 322/sshd
tcp 0 0 :::36666 :::* LISTEN 516/kodi.bin
tcp 0 0 :::36667 :::* LISTEN 516/kodi.bin
tcp 0 0 :::9090 :::* LISTEN 516/kodi.bin
With that setup tvheadend is not bound!!
Any more ideas?