Wow... that seems weird. Have you tried with an actual player? It's kind of difficult to pinpoint why that happens without seeing the code. There might be others here who have experienced this specific bug though.
Ya, no kidding. I'm good with finding any trigger errors. I don't know how to look at variants, but if it is a trigger error, then I'll find it. If not, then we can deffinitely narrow it down to variants.
I just had something like this happen for me, and I remembered this post. I had done 'Show/Hide the world' in the UI trigger section to Hide, did a few things and then it was supposed to Show again. But I forgot to delete a Hide Game UI trigger and replace it with Hide world. So it was hide world, do stuff, show game UI. When I ran this, it brought up the credits like in your video. When I replace Show Game UI with Show World, it went away.
So to test the bug, I put a Show Game UI action without ever hiding it. This brings up the credits. I'm pretty sure thats not intended. Do you have anywhere in your code that might Show Game UI even though it's already showing?