DVR Network

I have 3 DVRs set up on my DVR network.  1 master 2 slave.  Everything seems to work for about  week, I can see each DVR and play back recordings on any of the TV's.  Then something happens and I loose the network.  When this happens I can only view recordings made on the TV I'm watching.  Calling customer service and having them do a reset of the DVR's has worked each time, but this is a recurring problem.  I need a reset every couple weeks to get the network functioning again.  What could be causing this issue?  Is it a DVR issue?  I've had 2 replaced and it still happens.  Is it the wifi router perhaps?  It's also a Cox box, and been replaced once as well.