I know this topic is a duplicate of another post (Looping video flashing) in this forum, but as this is closed already and there is no further discussion or problem solving, I want to share that I am having the exact same issue.
I now experienced that this problem is gone when I feed in the video component with a mp4 that does not have an audio track. Tried different bitrates as well, but its always the same: If the mp4 contains an audio track, the loop is flashing or flickering. Maybe this will help to find out the problem behind this issue.
Is it even possible that the audio is causing flickering or black/whiteflashing between the video loops? It also happens in this repository when I load my videos, so its not just related to my project: https://github.com/expo/video-background-example
Looking forward to reading some suggestions / ideas!