Scene Transitions Not Working and Vanishing

I'm working on a video and when I add a transition between scenes, at first they simply don't work. After a minute, one or two will function, but beyond that they simply won't animate between scenes.

Removing the transition, adding a new scene, removing the scene and re-adding the transition, changing the type of transition, using a different browser, using a different computer and a different browser, using a different video; nothing fixes the issue.

And everytime I move to a new browser/new window/computer, all of the transitions have vanished from the video entirely. Simply aren't being saved into the video itself.

The one or two transitions that do seem to work also vanished when I downloaded the video.

Fortunately, I have Premiere Pro and can actually create real transitions, but it's a pretty big pain having to recreate the work and add in a ton of time to the video scenes to make them look clean.

Thanks