Hello,
I'm sorry you're having trouble with that, that would be frustrating. I have only ever seen this happen in one of two scenarios:
- The upload connection was too slow
- Apple Safari is being used
After you record the video, you can right-click and select to save the video. Then, using a different network connection (ideally a wired one), you can try uploading again. You could also try in a different browser, clearing your cache and restarting your device.
If all else fails, you might consider uploading your video to Box, Drive or some other service with a note to your teacher about your tech woes.
I hope this helps, and best of luck to you in your classes!