Strictly a hunch because I saw this in the 18.04 beta but it went away. Only when I set IPv6 to “Ignore” did I get IPv4 connectivity via DHCP. This is on the default connection called “Wired connection 1”.
Hey, can you tell me what kernel version you are running because with 4.15 and above my Thinkpad T430 with Intel 82579 loses ethernet connection after a couple of minutes or less. Thanks!