nginx and php (fast-cgi) hangs the connection

[yacenty]

Hello
from about month (moving to the nginx 7.61) I had a very big problem.
My server suddenly stops to serving dynamic content.
Static files are handled in regullar way but asking for php files gives nothing in the web browser, and sometimes in the benchmarking site in ab we receive broken sockets.
Some days ago I had moved to 7.62 and spawn-cgi 1.6.3 - then I thought everything is solved, but I realized that site hangs in the peak of the site.
There is nothing in the nginx logs, nothing in php logs.
What could I do?
What could be wrong?
Could You help me somehow?

Best regards
YacentY

Posted at Nginx Forum: http://forum.nginx.org/read.php?2,14052,14052#msg-14052