The same issue with Vontar X96 Max 905X2 4/64.
Workaround , but just 100M:
CoreELEC:~ # ethtool -s eth0 speed 100 duplex full
Then ping is working and hope streaming movies as well (i am not at home right now)
We must wait until someone fix the issue inside the driver:
CoreELEC:~ # ethtool -i eth0
driver: st_gmac
version: Jan_2016