Thanks for posting!
Based on your description of the behavior, it sounds like the the problem may lie in the network infrastructure somewhere outside of the dock. Given the behavior is somewhat intermittent, the first thing to double-check is that the Ethernet cable itself is not the cause by replacing it with a brand new cable.
If that doesn’t help, please keep everything connected (even though the Ethernet connection is not working) and send the output of our diagnostic utility PlugDebug --> http://plugable.com/support/plugdebug to us directly at firstname.lastname@example.org with ‘For Ticket 190680’ in the subject line.
This will allow us to match everything up and examine some log files from your system to help determine the next steps. If you could also include your Amazon Order ID number in your direct email (don’t post that or the PlugDebug here) that would be most helpful.