everytime I try to upload a new profile picture at GitHub it returns the given error message, no matter if png or jpg, no matter what size or browser. Any ideas?
No clue here, you might want to contact GitHub Support for private problems related to your account.
I am having the same problem, and by using Chrome dev tools i see that, upon trying to upload the picture, the related service replies "503 service unavailable"
Using a smaller image and changing from PNG to JPG worked for me when I ran into this.