Graphics mess up export from m4v-files
Every time I have an m4v file and export with some kind of graphics from Essential graphics, the export renders with very poor quality and light change for the duration of the graphic. The rest of the video turns fine, it is only during the graphics. It doesn't matter if it's a Mogrt that I created myself, or an Adobe Stock mort, or just text that I add in Premiere. This ONLY happens if the original video is m4v. If I first export the same m4v to mp4 and then add the same graphics to the mp4, it looks fine.
I have mainly tried exporting in h.264 and High Quality HD 1080p, but have also tried higher bit rates, different render engines and maximum render quality, and it is all the same. I use an iMac, 64 GB RAM, Mac OS Catalina. Premiere Pro version 15.2.