After a big problem with the newest ejabberd-version and sleekxmpp I located the problem in ssl.wrap_socket. When called with no parameters the later do_handshake (method of ssl.SSLSocket) fails with an exception. When called with keyword-parameters which match the default values (except for do_handshake_on_connect), do_handshake will fail when called after that. Once I have time I will edit this post to add the required information here, but for now I refer to the issue filed on github: https://github.com/fritzy/SleekXMPP/issues/452
The important information is in comments 2 and 3.