I'm getting missing media between frames

Hello, new to video editing here. As you can see, the red screen flashes for a moment at the beginning of the video and then again when there is a cut at 2/3 of the video. My timeline doesn't show any problems, there aren't empty spaces between cuts or at the beginning. The red screen seems to be not immediately as a first frame of the clips but a couple of frames after. Going frame by frame it seems to be mixed with the image, not showing by itself. To obtain the clip I've been stretching and reversing at time a video of about 2-3 seconds, and used optic flow to intepolate (if what ChatGPT said is true).

I'm using the free version of DaVinci 19.1.4.11

Edit: I see I can't attach urls, hope this is understandable without the video