Channels DVR recordings recently getting de-rezzed?

Recently, many of our Channels DVR recordings have been almost unusable due to 'de-rezzing'... by which I mean the digital signal appears to get corrupted and the image is unviewable. I have noticed it is much worse when two programs are being recorded at the same time.

This didn't use to be a problem, but I have been trying to diagnose a general slowness in my computer recently and so it is possible this is related to that.

Is there a way to tell Channels DVR to only record one program at a time?

I think that is possible with the m3u sources but I don’t think so with other sources.