Strange Ajax Problems

[Leon Kellermann]

Hello :)
I just migrated to Nginx with php-fpm. So far everything ist running quite
smoothly expect our Ajax-Chat (https://blueimp.net/ajax/ )

If i load page first time, it won't request any data via Ajax. Nginx returns
only blank data. 
After second Refresh the whole Site is blank until i clear Cookies. 

So far i found no corresponding errors in the log ( Log Level debug ).

Anyone has any Idea?

Regards,
Leon