That is odd, considering it now works for me in a completely stock project, even with only a single video splash.
It's possible that the issue is that your core files are also out of date, from somewhere between 1.0.2 and 1.8.0, and that they'd made some changes to the scene load order in earlier versions, before settling on what they have in 1.8.0.
First I'd check to see if an image splash works, to see if it's something weird with the video specifically. If that also doesn't work, test it in a brand new project, and then compare the versions of the core files from your project with the new one and see if rmmz_scenes.js is out of date (although be warned updating it might break other things).
If the image splash works fine but the video doesn't there might be something else going on with it. Try playing the video using the event command in game and see if it will play there, if it won't the format might be something that simply won't work in rpg maker for... some reason. Like I've said to some other people in the past, I didn't do anything fancy to make it play videos, just hooked into whatever the engine already uses to play them in game, so I'm not really in control of what works and what doesn't, unfortunately.