Ok, I have figured out what happened but it is still a bug. When I installed the program, I installed it to my account (not admin) using the admin password to verify, as normal. It turns out that all of the AppData installed to the other account and not mine. So when I set everything up yesterday, it was saving into another user's AppData folder and I was using it from there. Now, after a reboot, I am using OBS Studio from my AppData folder instead of the other accounts one. But nothing was set up in my AppData folder, so I have none of the previous settings etc.
Now that I know what I am doing, I have re set up OBS Studio in only a few minutes.