It is probably something to do with your PC/Mobile. Twitch videos especially don't play in Windows Vista. :P
The refresh button looks like this (at the upper left corner):
https://qph.ec.quoracdn.net/main-qimg-ae92b32bf2255fc758cf0ea8e4b76b18-c
Or use F5.
sometimes some twitch videos wont load because either the channel has been deleted or the vod wasnt highlighted (twitch deletes non highlighted streams after like a month)
Can you link me to a run where this is happening? It could be a http embed, which doesn't work on the now-https site.
I use both Twitch and YouTube links when I submit a run. :P
https://www.speedrun.com/run/zxvl9vky (at least this was the first time I did it.)
The first 2 worked for me, the third one didn't which is odd. Might have something to do with your internet probably (and mine too).
Twitch added name changes recently and that changed the links to highlights, I think all of the old links are dead by now but maybe some still work, you just need to find the new link.