Thanks for your help.
The problem is showing up on all 3 wireless boxes, and they were all changed last week, along with the PVR, the modem, the VAP, and a new service line to my residence. So hardware problems are pretty much ruled out.
What you are saying makes a lot of sense, some network interference.
No new electronic gear has been brought into the house, and nothing has been relocated.
While rewinding on the PVR does not cause the problem, if I rewind on a wireless receiver, the recording will be affected.
Any idea where to start looking on the network?
I tried shutting down all devices that are using WiFi in the house, and that did not help.