I installed all the stuff necessary and with out fail it just worked. Even with multiple replay files, no issues. If you add the slow motion plugin and set it up you can get the replay in slow motion. I've used this feature now in 7 or my son's soccer games as they are being live streamed, much to the enjoyment of the viewers.
I had no issues with the OP's instructions. Everything worked as described. Only thing I did differently was checked off the box to close the media source when it's not active. Each replay saved as a separate file (great for highlights later) and played correctly.
Guys, there is an easy solution to your problem, he unfortunately doesn't mention it in the guide. This will only work if you don't care about recording your broadcasts. If you go to Settings|Advanced, under "Recording" you will see that it does filename formatting that puts a date/time stamp as the filename. Remove ALL of that, and have it simply save the file with the "Replay Buffer Filename Prefix" set to "Replay". This way, every time it saves the replay buffer, it will just overwrite the the file, instead of creating a new file with a new filestamp. You might also have to check off in the media source to "Close the file when not in use" if you get any sharing violation issues.
I was having the same issue as you guys, once I did this, now I can easily just press CTRL+SHIFT+S and then CTRL+SHIFT+R and it's always my LATEST recording, because it just keeps overwriting the same file. Hope this helps!
If I had to guess, the instant-replay.lua script is meant to replace the Media source with the latest Replay Buffer video but that simply doesn't happen and the original video is played. This resource does not work.