I've seen the problem before but it was a lot worse when I tried to watch a film (Churchill) on 10th August. Bad enough to make it unwatchable.
Every few minutes the picture starts breaking up or freezes. Eventually the sound stops too. Sometimes I could clear it by fast forwarding or rewinding a bit but it did the same again soon after. Sometimes the app freezes and the box reboots (3 times when trying to watch the film).
My broadband speed is fine (box is hardwired). Other apps work fine.
Anyone else having this problem or know of a fix?