Nginx request to apache timeout

Nginx request to apache timeout

I have a server which uses WHM, Cpanel, Nginx and Apache.
Nginx was added using the nginx admin plugin. It has been working fine for
several months until today.
My server has been down almost all the day, running "top" shows hundreds
of Apache processes (httpd processes) at first it thought the server could
be under some sort of DDOS attack but looking carefully seems like all
those processes are request that nginx send to apache and that for some
reason just halt without timing out or anything and are eating all the CPU
and RAM.
Earlier the Nginx Admin UI was not working and I used the "Check/Repair a
Perl Script in WHM" section on WHM to make it work, but it seems like that
did not fix the problem.
What could be happening?
How can I uninstall-reinstall nginx?
Thanks,