Just like to say that if you are using opfine on your forge pack Please Be Aware they is many bugs that can occur with settings
Like Fast Rending if you had it on then turn it off while editing
you will get a invisible gui and world
here's a video of what happens if you disable fast rending while in the replay mod editor
https://youtu.be/4cJfc4biL1k
Just like to report this so bugs can be fixed!
also fast rendering can cause black render for replay mod