503 Service unavailable

I am encountering this problem and I don't know how to solve it.

I have a PHP script, which in the past worked for me without any problem on the same database, same environment...etc...

But it was on another host and another panel...

I launch it, it works, and from time to time, I get this error message, 503 service unavailable.
If I change a number in the url (what it does is that it imports data from one site to another) it continues without a problem.

After a lot of searching, the only error in the log I see is:
"child 4484 exited on signal 11 (sigsegv) after xxxxx seconds"

I have increased the times (set to -1) resources in php, in php-fpm I have set:
"pm = ondemand
pm.max_children = 100
pm.max_requests = 10000
pm.process_idle_timeout = 900s"
I did get that the max_children was low, it was advisable to raise it, but it was not the error.

I deleted the error log, I repeat the process, and the only error that appears is the previous one, signal 11...

I've been like this for 1 month or more, and I'm desperate...

Any ideas?

Did you check (and increase) max execution time, memory limit, etc. in your php.ini?

Did you check (and increase) max execution time, memory limit, etc. in your php.ini?

Yes, was the first I was try.
In this moment, I have this values:

('memory_limit', '256M')
('upload_max_filesize', '128M');
('post_max_size', '256M');
('max_input_time', '-1');
('max_execution_time', '-1');
('default_socket_timeout', '-1');

And I try with 512M, 256M and 512M (in the order, mem limit, upload max, post max...)
Also I try with 1024M, 512M and 1024M.
Same result all time...

Thanks for your reply.