Hiya- I actually already fixed my "Television Signal Has Been Lost" problem - but I thought the solution might be of interest to others. (I also caused the problem in the first place, so it is a cautionary tale as well!)
Set up is an ActionTec 3200M router hardwired to a UIW8001 and UIW4001 STB (2 Tvs). Starting a few days ago, turning on Optik Tv on either TV would display any channel for about 10-15 seconds, before the video would freeze, and the "Television Signal Has Been Lost" screen would appear. Restarting the router and STB resulted in the same behaviour.
Called Telus phone support, and their remote attempt to reset/troubleshoot had no effect. Telus tech visit scheduled.
I did some more looking around on this forum, and noted discussions about switches and non-Telus routers causing the same kind of video loss because of IGMP snooping being blocked. That lead me to recall i had changed that IGMP setting on the ActionTec router about 3 months ago, to try to fix a connectivity problem with a wireless audio device. I changed the setting on the router back to "snooping enabled" and "standard", and voila, Optilk TV worked normally again, and service call was avoided. Seems odd that it took 3 months after changing the setting for Optik TV to have a problem, but i assume there is probably a technical explanation.
As an additional note, I have had both STBs running without problems for years while connected through unmanaged ethernet switches - i.e. no IGMP problems have been caused by the switches. Happy snooping!