Hi! I’m struggling with preview generation too - but have not tried to limit it as you do.
My problem is the extremely high disk usage of the generated previews, so I will try to do what you do; only create previews for images.
I’m wondering if you maybe have old previews from before you limited preview generation to only PNG, JPEG and GIF?
You can delete all previews and generate them anew. That’ll take a while of course, but maybe could fix the issue?
Here’s a few potentially useful links: