In this video we can see some of a flicker bug I encounter: https://www.youtube.com/watch?v=0uTAcJBhhZk
It happens on the red cape at 3:25 and a few more times in what follows mostly when the footage shows a dialog being brought up or closed (like at 4:15 or 5:24). It also happens within Shotcut itself in the preview. It seems like it’s a chroma-related adjustment being done and that sometimes the non-final version of the frame appears both in the preview and in the render, as if it was an intermediary state of the frame wrongly used as if it was in its final state. The YT video above was rendered with “0” threads (renderer was software x264, but I don’t think it matters much), when rendering again with only 1 thread the problem was still present but less so, and not necessarily in the same scenes, so for instance in the latter render the red cape at 3:25 doesn’t flicker anymore.