There are multiple factors that can cause this issue. Could be a problem with the internet or it could be a problem with the connections to your set top box. It's best to contact support for troubleshooting assistance as a field tech visit may be required.
I have had this same issue for almost a year. I have had numerous technicians come out to “fix” the issue, so far nothing has helped. Frustrating and very annoying. They are now sending out a “senior technician “ next week to see if they can fix it. Sorry to hear you are having issues as well.
When I had this issue it turned out to be a bad gigabit switch I had connected behind my PVR. Nothing else connected to that switch had issues. Once swapped out, the problem went away.
On this subject, I got a survey request from Telus yesterday. The focus was on Optik Tv and several questions on the picture freezing, macroblocking and other picture quality issues. Looks like they are taking this seriously. In my case however, I have had no problem for at least the last couple of years. So, I answered the survey questions to reflect that. This will be a good opportunity for those who have had troubles but haven't called Telus yet to let them know.