Those screenshots are helpful to understand what you are doing here.
You have already set the video properties to the settings I would use for most stable.
In trying to diagnose and fix the issue, I always try to go to the simplest possible option first.
In this case, that would be coping slides 2.6, 2.7 and 2.8 in to a brand new project.
I would then ensure any unnecessary triggers are removed.
In your case, this would be the Slide 2.7 "set state of next button" triggers (x2)
Its unlikely they are causing any problems, but Ive seen Storyline bug out at simple things like this before, so I would remove it.
Then publish your new 3 slide test project using LMS publish option, and ensure you are saving it locally. Dont use the cloud you mentioned for anything to do with the test project.
Can you try that and let me know how you get on?
If possible, and you can email me the video file, Im happy to run it through some programs here to test the video itself.
