Yep, I sometimes also have the problem. Especially with .psd files (Photoshop Files). I am not sure if it has problems with upload semi large file sizes. (I also had the problem uploading a jpeg Panorama Photo with 8 Photos (50 MB).
But I must say. I have bought CC 3 weeks ago and the problem was often just after I bought it. It got better over these 3 Weeks.
I just tried to upload a 468.2 MB movie and it didn't work: