If Carlos' suggestions don't fix this, go to that spot on the timeline. Figure out what's the problem ... remove and redo some effect, or even remove the clip from the sequence, delete from the project, close/reopen PrPro, then re-import the clip into the project and return the section to the sequence.
The pixel ratio and the image size of the imported video file (let's call it video X) were not matching those of the sequence, nor those of the other videos previously imported in that sequence (videos Y, Z, etc).
Solutions: - Change the sequence settings of video X and export it again, then import video X where you need, or
- Import the sequence of video X in the project where you need it. Even if image size and pixel ratio are different, they will be encoded correctly.