I Have also the login 1 click problem with version 2.3.8 and 2.3.9
My config is: windows 2008 R2 Server with IIS 7.5 and PHP 5.3.8
All my rights on ntfs are OK > change rights on de whole website
Sessions are generated and no errors apear in de error.log
Time zone setting is OK
PHP functions full, because i'm also using other php sites on this server.
When i install 2.3.7 everything works correct, so for the time I switched back to this version.
I can't switch to apache because i'm using also ASP for other sites on the same server.
Hopefully the problem can be resolved, because i don't know what to changes or test anymore.