YouTube – Contacting Support for Unfairly Removed Videos

The playlist is available in the current design (One Channel, which you're referring to as "new design") if the user has featured a "newest video" shelf on their channel page – click the "play all" button.

In the now-new design (Material Design), there is a link to play all videos on the /videos tab of any channel.

This is not a bug. YouTube is experimenting with a new player which is resizing the Player Dynamically. Read here: YouTube Experiment

There's a new YouTube experiment that changes the video player's size, depending on the browser window's size. When resizing Chrome's window, YouTube switches from 360p to 480p and to 720p, while the player gets bigger.

Are you sure you deleted all your cookies ? Try this, launch your Chrome Browser in Incognito Mode (Ctrl+Shift+N) and go to YouTube and check if you still see the large player. If not than you did not clear the cookies properly.

Regular YouTube Player

To go back to the regular interface press Ctrl+Shift+J in Chrome and Copy/Paste in the console the following code:

document.cookie="VISITOR_INFO1_LIVE=; path=/;
domain=.youtube.com";window.location.reload();

Large YouTube Player

To set the large YouTube player press Ctrl+Shift+J in Chrome and paste the following code which will change the YouTube cookie:

document.cookie="VISITOR_INFO1_LIVE=E_OLzg3yeLw; path=/;      
domain=.youtube.com";window.location.reload();