Connection drop issue

Situation:

2 new MA2500D, firmware version 2.0.16. One endpoint in a device, the other endpoint in a gigibit ethernet switch. No splitters, no modem on the coax - using existing, no longer used coax to wire one part of the house to another (replaced a splitter feeding two segments with a female-female connector to create a single line). Things work fine for about 10-15 minutes (streaming to a Roku in this case), then simply fail. When I unplugged the ethernet from the roku and into a laptop, the connection appears unusable to a browser, while allowing ping and ssh to another machine attached to the switch at the other end. This half-live state persists for a short time before returning to normal behavior. This sequence of events has repeated several times.

Any ideas or explanations for what I'm seeing?