Yes we updated a file iv-includes/include/functions.inc.php, sorry I did not get back to you earlier. We will be updating this file for the global download.
To be honest, I don't have the exact technical details, because our colleague that works with the former X2 and also fixed this, is not working directly with us any more. It is definitely related to the AUTH, but also server and sessions ... Therefore, once it was "fixed", it is likely it cleared an issue in your session so that the non-updated version would have worked also.