Seems if there is an issue with MTS "Ultimate" tv I will encounter it, the black flashes included.
Based on a significant failure at one point I know the service is basically a large computer network as at one point by box said soething like "network connectivity lost" even though the cable was still connected on both ends.
That said, I have the black flashes on pretty much every channel and used to actually get freezes on the classic service occasionally. Last night a very noticable one (ie several seconds long) happened on Global Winnipeg during the 6:00 pm news. This flash was so long my tv actually reported "no signal".