It's an Acer Veriton M480 Intel Pentium E6700 Dual Core 3.2GHz 8GB RAM Gigabit Ethernet, new 4TB WD Red data HDD and 320GB system boot drive. It was working fine with the initial install. Problems only emerged after attempting to update the Plex release version.What's the hardware you are using? Motherboard, Ethernet chip?
The Ethernet cable is also OK - can ping the system and the dashboard indicates all's well: