I think I have figured-out a bug, and how it may be fixed.
I have not been able to use my LAN connection. My computer is an HP 17" pavilion model. What happens is it works properly on first boot, but after going to sleep, it loses my connection and won't connect again about 99% of the time. It does work properly from wake on wifi.
I became frustrated, and installed the trial of Xubuntu to see if this same problem was there. It was also a problem with Xubuntu, BUT what I found was that under Network Connections/Ethernet Connections 1/Ethernet Tab, Xubuntu allows me the change to edit the "Cloned Mac Address" and change it to Random. This seems to solve my problem in Xubuntu, however in Ubuntu-Mate, I am not given this list of pulldown options from this menu. They seem to be completely absent. There is only a blank for "Cloned Mac Address."
I might also add that I on the same page, I changed my MTU number to 10, but I don't think that has anything to do with it.
Do you have "automatically connect to this network when it is available" marked in your DSL/PPPoE connection settings? If it's enabled, the connection should be established after some time.