After switching from apache to nginx + php-fpm, a strange problem began for a specific user. What could be the problem?

Question

PHP

Greetings! I ran into a very interesting problem. After switching to nginx + php-fpm, only one user had problems with the project. The server responds to many of its actions:
NetworkError: 500 Internal Server Error
At the same time, nothing is written to the logs.
At random, one of the problems (loading the map) was solved. In code

<? foreach ($map as &$hex) : ?>
...
<? endforeach; unset($hex); ?>

the pointer was removed, after that the 500 error disappeared.
But the rest of the actions still give error 500.
I emphasize once again that only one user has a problem, the project works without problems for everyone else.
On a local server with Apache for this particular user, everything works like clockwork.
I sin on some strange errors with memory in php-fpm.
What could it be?
Thanks in advance.

Answer 1

what does phpinfo() say about display_errors?

Answer 2

Enable php-fpm logging and read its log. Enable logging in nginx with debug mode, and read it. There was a similar problem due to the FireFox extension - FirePHP, very large headers were sent in response and the server responded with an error. Cookies have nothing to do with it, the useragent was guilty (the FirePHP text is sent in it, this is how the extension works), so try connecting from the console via curl, for example - read the logs, see the headers.

Answer 3

Is the user's login by chance something like "';DROP TABLE "? :)

Answer 4

Thanks everyone. Codeigniter has error logging, for some reason I relied on it.
But the type error Fatal error: Allowed memory size of 33554432 bytes exhausted (tried to allocate 78 bytes)
remained in oblivion.