Animate won't export full video

Hey!

The file I export is always corrupt in the sense that the beginning of the animation works up to a specific point when it just freezes. Everytime I reexport or export just the end to make amends for the "missing" part of the video, there's still a random amount of animation that just doesn't render. (I can tell because the file sizes vary even when exporting the exact same thing.) Why?? My settings are all default (it's all German on the image, I'm hoping you can still unterstand 🙊), the canvas is regular UHD. Even when I check the SWF movie, the whole video plays. I've been searching up and down the internet for a solution – can someone help me??

Thank you so much!