Okay we are having the same issue.
Are you able to change your skin? Because I am not able to do that as well.
I have tried all of what you are suggesting. I have tried it on multiple computers and at the end the results are the same and it is not allowing me to connect to any server.
I have tried all these steps and non of then seem to work. I end up getting the same error message. I have even tried it on Linux as I use Windows and it still does not work.
This is what i am getting every time i try to join a server.
When will Mojang fix this bug? I am not able to connect to any of the servers and play minecraft and it is quite annoying. I did not expect this from a game that I had to pay for.