i don't own a X8HP but a X8H.
with the x8h the fixed ip is solved.
about the x8hp , i need your return.
if it was solved with the x8hp 18.1 img, you may replace the dtb in 18.2 tar or gz with the 18.1 one's and update your device.
i guess it will do the trick.
At X8HP = As I recall, in the Kodi 18 Final version I set the IP address manually on the LAN in the libreelec settings and this version 18 kept the IP address but changed the MAC address after restart or shutdown.
And as I wrote in version 18.2, Wi-Fi keeps both IP and MAC and can be permanently reserved in the router.
Versions 18.1 and 18.2 on LAN with DHCP do not hold IP or MAC and cannot be reserved on the router.
I'll try to help with X8HP