If, like me, you're creating a large video portfolio site (over 50 vids) in Edge, you may find after a while elements on the stage start to vanish (they're still there but invisible) and the program REALLY slows down. And lots of crashes. I've asked the experts and the response generally seems to be "Site's way too big!" HOWEVER, I have a good workaround:
After importing a Mpeg4 and Webm file into the video library, put it into your design, animate it, add functions, preview it, etc - then DELETE it from the media folder! The elements remain with all the attributes and code attached on the timeline, stage and elements window - but it's just a placeholder. Once you've done this, you can move on adding more and more videos, repeating this process. The project file never gets too big or slow! Then right at the end, put all the Mpeg4 and webm files back in the media folder. You might not be able to launch the project and preview (it'll be too big) but you can still drop it on your browser to check. And, if all's good, upload. If there are things that still need fixing, take the video files back out the Media folder so that when you launch the project file again to make amendments, it'll run smoothly. After fixing, put the videos back.
Hopefully in the next full version, Edge is made more robust and able to tackle.