This layer will render at one resolution and then your mixed resolution timeline should go through Media Encoder 2018. One work around (which we used at the time of the red frames), is to throw an empty effect layer on top of your entire sequence. That was finally resolved with a Media Encoder update, but now seems to be back with this new version of the same issue. Several versions ago of Media Encoder, it would freak out with mixed resolution Quicktimes and put solid red frames whenever the footage was different from the first frame of the Quicktime's resolution. App Name: Adobe Media Encoder: Developer: Adobe Systems Inc: Version: Adobe Media Encoder CC 2020 14.0.1.
I just tried a test replacing the DNxHD115 slate with DNxHD175 version of it, and it went through perfectly. Therefore, you can find out if Adobe Media Encoder will work on your Windows device or not. I went back to Media Encoder 2017 and it was not a problem. Each exported Qucktime would come through Encoder as solid black. I usually work at DNxHD115, but I made a quick edit of some DNxHD175 footage, but the timeline still had a DNxHD115 slate on it. It sounds like we have a similar set up to you. I just ran across this recently in my own workflow. In this solution, we will completely remove the Adobe CC Products from your computer and then try reinstalling them again. I believe this is a mixed resolution issue. If all the above methods don’t work (no matter whether you had Adobe Media Encoder installed or not), the only logical explanation is that your CC products are corrupt or have improper structure.