My error was the same:

Error: The remote NX proxy closed the connection. Error: Failure negotiating the session in stage '7'. Error: Wrong version or invalid session authentication cookie.

I solved it in my case.

The reason was a wrong writing permission in the appropriate directory where the client logged in. This is certainly not a bug but a mistake, - and a trace to look at for the the one or other case with this error.

Regards,

horst