I set it up to play a playlist with 20 videos in it and it only displayed 4 of them; and they were in the wrong order.
It's funny, I used ytplaylist.com myself, and I find it hard to create new playlists because it seems like they have a way of identifying my computer (my browser deletes all cookies upon exit) and displaying my last playlist every time I go to their website. So I quit using them.
The order that this plugin displayed the videos is the order of the playlist that I last made on ytplaylist.com, but it does not even have all the videos I left there.
I am not going to have much time to troubleshoot this with you (it looks like you offer pretty good support here), I am writing this more as an fyi.
I like the idea of having the playlist itself displayed in a scrollable window at the side; but the main problem I have with this setup (even if it actually did show all the videos) is that it is not responsive, so it does not show well on mobile devices. (This is true with almost all WordPress YouTube plugins)
I obviously cannot leave this live on my site, so it would not be of much use for me to leave my url (http://www.apopvids.com/ ;), but if you think you have an idea of what was wrong with my installation, or if this was a complete anomaly, feel free to change this to resolved.
Anyway, I think the basic idea you have here is a good one, and I thank you for developing this plugin. Best of luck in its further development.