Alpha Key Issue

Quick question, I have the ATEM Mini Extreme Iso. When I turn on my downstream key for alpha channel, there is a pink dotted line that appears on the left side of my output screen and across all feeds like livestream and monitor. What is that, and how do I get it to go away? I hate that it appears on my tv's and streams.

What is your source, and how is it getting to your ATEM?
If you're using DSK, then I'd check your two inputs (key/fill) and see if you see that line on them. For example, if key is 4 and fill is 5, then I'd take each of those live and see if you have that line on Program. If you don't (and that area just appears all black) then I'm really not sure. Maybe you can adjust the masking for that side of the image (I've never tried that on DSK, only on USK).