Video Quality Issues After Upload to YT

Hello,

I have just finished working on editing this video and uploaded it to YT: https://www.youtube.com/watch?v=xjj3S2UdYq8

It was filmed with a Hero 4 at 720p – 30 fps. I used Adobe Premiere Elements 13 to do the post-processing (rendered at HD 720 – 29.97 fps setting), but what I am realizing is that the YT video (when running at YT's 720p setting) still looks nothing like the file on my computer. As you can see in the video, it starts out looking somewhat clear, but then has these extreme fits of pixelation (for example at 0:21 and 0:37). I have filmed with this GoPro at these setting before with no issues (see other videos on channel) and I don't think it has to do with the vibrations in the video because the file on my computer looks just fine in these sections. Can anybody tell me what I am doing wrong?

Thanks, 

Jeff