Sometimes a channel will use their own placement container using workarounds or non-standard implementation. This means that the containers can "break" when trying to improve the end user experience.
All channel placements are added on top of the page and then positioned relative to the absolute size of the feed.
This method is often used purely because it's easier to add to the ad system. A less experienced developer will often use the easiest method to add the placements at the end of the page then use "hacks" to position them in an absolute manner in-feed.
How To Fix It
Disabling the responsive option for the tag - this will prevent the tag from modifying its environement and will force it to use only the given placement dimensions.
If the provided size or the placement itself is broken, please contact support