Missing Data / Dead Pixels in Media Encoder Exports

I have certain presets saved in media Encoder that I use quite often for certain situations. No issues with them, but then every once and a while, I start seeing missing data information in the video (that LOOKS like dead pixels, but I know is not the actual pixels since that would refer to the monitor, not the export).

Why is it that a preset that I use will work, then randomly, all my videos have had missing data that almost looks like I added a film grain effect to the video?

Any help is appreciated!