Been having a problem with my 80D over the past two weeks, primarily on video - a cloudy spot in the upper left of the frame. The problem is intermittent. It also appears sometimes on stills. I've been shooting with an 18-55 zoom. It doesn't appear to be sun flare. I've checked the lens and cleaned the sensor. Yesterday, I grabbed my T5i with a 50mm, along with the 80D, and went outside and shot test video using both lenses on both cameras and couldn't get the 80D to have the problem. I use the 80D for my job and can't afford this glitch. Any thoughts? Here's a link that will show a video where the problem can be seen: https://wheels.rep-am.com/2020/08/my-ride-a-corvair-that-bucks-its-bad-reputation/
Could there be a spot on the rear lens element? The fact that it shows intermittently makes me wonder if you have a greasy finger print on the glass somewhere which only shows as you open up the aperture. Vintage movie makers would put grease around the front lens filter for a similar effect...here is a example. https://lifehacker.com/use-a-dab-of-vaseline-to-take-vintage-style-photos-5624416
