I have had this problem as well just yesterday and am looking for help. Haven't found a solid answer as to why this happens but for me it has something to with the vignette settings on the lumetri panel. If you turn off vignette you'll see the dot go away. I haven't played around with it enough to know what parameters to set it to so that it doesn't happen but will post it here once I find out. I hope my answer helps you in some way shape or form although it is almost a year later, haha.