Hey there,
I am really sorry for the delay of this reply as it is a public holidays for us here.
That was strange, it seems like only happen on your video which using this video format .mov , if you try my attached video (you have to extract that zip file), it upload just fine.
Based on what troubleshoot, encoding part already completed but when it switch to show the video status, it will hit 500 internal error, it might be hitting one of the php error but your server already override that PHP error to show 500 internal error.
May i know is there a way to consult with your webhosting provider and see whether can temporary disable this 500 internal error so we can see the exact PHP error what it hitting?
Or do you have your server error log?