I have an MiniMX S905 2GB/16GB ROM. yesterday i updated it from 8.0.2e to 8.1.5 and i have immediately lost the use of Ethernet.
Now i get an IP address but its not correct and i do not get any internet access.
however Wifi 2.4 and 5 work perfectly fine.
Perhaps double check LibreELEC Network settings. Perhaps double check cable or switch port.
If no luck, does downgrade to 8.0.2e make Ethernet work again?
If not there may be a physical issue. Could be cable or switch port. Or (hopefully not) MX port.
Good luck (I have the p200 MiniMX-G too)