especially larger files fail a lot, since my connection isn't the fastest (20-30mb/s), it almost feels like there's a timeout thing happening.

I tried using Opera GX, Chrome and Edge. It's consistent throughout all browsers. I wanted to edit the name of an Illustrator file of 1.7Mb. When entering preview mode it is fine when the preview is still loading. But when it's "done" loading, it displays an Icon which probably means the file can't be previewed caused by lack of Illustrator support (I presume?). So both the browser and the desktop app freeze when that happens.