I've had the same issue with a timer for NBC Nightly News. I noticed it didn't record one night about a week ago, looked in the daily schedule and saw it was marked "Canceled by user". Nobody was watching TV at the time, so I hoped it was a one time problem. The Hopper did record three other programs at that time, but the Nightly News timer was the highest priority timer. Next night, I checked at 6:31 to see if it was recording, nope, again recording three other lower priority shows, says "Canceled by user". Deleted the timer for Nightly News, created a new one, marked it #1 priority, next night, same thing.
Well, I noticed one of the shows it was recording at the time was a kid's show my kid never actually watches, so I canceled that timer, and lo and behold, Nightly News started recording. Worked fine for three or four nights.
Tonight, Nightly News didn't record, and it again says "Canceled by user." Nobody was home at the time, so nobody canceled it. Also, it recorded two shows, and a third was marked "Canceled due to priority".
I haven't noticed this with any other recordings, and I scrolled back through the schedule and didn't see any others marked this way. I'm starting to think my Hopper doesn't like Brian Williams.