HPNA is more than fast enough to support multiple streams to multiple devices with no issues.
said by ynohtna: The house is 4 years old so it's not like it's really old cabling (maybe cheap ones).
Old cabling is rarely the problem.
A damaged section of cable, kinks in the cable, staples that have been driven in so hard as to crush the cable, improper terminations, improper grounding. These are all problems that can seriously affect coax performance even in a relatively new install.
Open taps, cheap splitters, or excessive splitting, can also cause problems.
Also, it is possible one of the HPNA devices is defective.
First thing I'd do is take a short coax patch cable and connect the DVR/STB directly to the router (you might have to temporarily relocate your TV). See if the issues go away. If they do, you've got an issue with your house coax. Start by checking the terminations to the wall plates.