I am running Mocha Pro OFX 6.0.2 within Fusion Studio 9.0.2 on Mac OS 10.14.3. My source video is a jpg sequence, and my clean plate is also a jpg.
I am seeing occasional frames filled in with a solid color when using the Remove tool. An example can be found at: https://media.davidb.org/animations/ex10-flashy.mp4 (this is exercise 10 from the Mastering Mocha 2 training). Another post suggests an issue with this occuring with the ProRes codec, but I’m seeing it here with just a jpg sequence, and a jpg as the clean plate.
Above is how I have the remove module configured.