We've been having problems with channels 4, 7, 17 and 18 not loading at all on our 4642 box.
We've had problems with channels 17 and 18 for a while, and a technician visiting and shortening the cables in our apartment does not seem to have cured the problem.
These sorts of issues are often related to a poor signal in your home or neighbourhood. Did the technician say that the signal was good? Here's a post on the topic. You can check the signal yourself using the link there, or you can call Rogers and have them check the signal remotely. Why was the technician there in the first place? Shortening a cable has almost no effect relative to other possible causes like a poor splitter or poor connection, etc. Perhaps he was just redoing the ends/connectors in case it was a poor connection. He should not have left if the channels were not coming in properly, or if the signal was poor.
A poor signal will usually also affect things like On-demand, SDV channels (the ones that are not sent 100% of the time and require a return signal from your box) etc.