Volume Issues

I've got an Xfinity XG1-P set top box, and two other digital converters in the house.  The XG1-P connects to our main TV, a Samsung TV.  The  Xfinity remote control is used to operate the Samsung.  The other digital boxes are connected to a Westinghouse TV, and a Vizio TV.  These TVs also use the same model Xfinity remote control to operate the TVs. All this was installed about two years ago, and all was well, until about a month ago.

The problem is with the volume.  On the Samsung TV, sometimes I can't move the volume up or down.  Say I've got it set at 50, and I want to raise it to 55.  The volume won't move up or down.  I have to turn the TV off, then back on, and when it comes back on, still set at 50, it's twice as loud as right before I turned it off.  But, I can now operate the volume.  Maybe a few hours later, I want to turn the volume down, but it won't move, so I turn the TV off and back on, and I'm back in control of the  volume for maybe a few hours.  I thought it was the remote, but it has full batteries.  Also, this occurs with the Westinghouse TV.  Weird.

I haven't experienced this on the Vizio TV (yet?)

I'm beginning to wonder if this has something to do with the main set top box, the XG1-P, since two TVs are affected.

Any ideas?