Welcome to the forum. I don't remember seeing anything like that, but someone else might. If no one else answers in the next hour or so can you post a file that's displaying that? (Click on the black text "Use advanced editor" at the upper right corner of the Reply box to post files, then there will be a link at lower right to attach files.)
menu: Photoview 360 > Render Region
Thanks for the warm welcome!
Ingvar is correct, it was the render region plane that was turned on.
Thanks for the quick response.