Picture and DVR freeze when trying to watch recorded shows

We recently moved the Cox Contour system with the whole-home DVR.  The main receiver is in our living room with the additional receiver in the master bedroom.  I have found that when I try to watch recorded shows in the bedroom the picture will often freeze along with all of the controls on the remote.  I have to just wait until it unfreezes and then I have to go through the process to chose my show again & resume where I left off.  Then when I do that it has skipped ahead in the program and I'm afraid that if I try to rewind it the show will freeze again.

When they installed our Contour they mentioned that we may need a wi-fi extender, would that resolve this issue or is there something else causing this problem?

Thanks.