@Hinderslyne I se a lot of complaints about this Channel 4 app. It seems to have a lot of trouble handling advert transitions to and from the viewing program. I see that too sometimes with other apps here in OZ. It is possible that their CDN (Content Delivery Network) servers are struggling. Best thing would be for you to log in to that Channel 4 site, and decribe your issues,how many times it happens per day, and what effect it has on your viewing pleasure. The more complaints, the quicker it gets fixed.
Check your network though: Are you using WiFi or LAN internet connection? If WiFi, is it 5GhZ or 2.4GhZ band? Does the signal strength look good on a phone using the same WiFi band as the TV, when you are near the TV?