Issue Cannot change pm.max_children in domain PHP settings

[charlesmass]

I'm having trouble understanding how pm.max_children works in PHP settings of a specific domain.
What I did :
- Websites and domains
- Scroll to my domain "example.com" and click "PHP Settings (v7.4.8)"
- Under "PHP-FPM settings", entered "200" as the value for "pm.max_children"
- Clicked "Apply" (or "Ok", does the same)

Although the value entered remains when I come back to the PHP settings, it doesn't seem to be taken into account in /opt/plesk/php/7.4/etc/php-fpm.d/example.com.conf.
And I get a lot of " WARNING: [pool example.com] server reached max_children setting (20), consider raising it"
Can anyone help me with that ?

I checked
- "Run PHP as FPM Application served by nginx" is enabled.
- pm is set to "ondemand"
- Changing other settings works for example.com (I tried changing "pm", "pm.start_servers", "memory_limit", ...)
- I tried setting the same value for another domain example2.com which is set as "Run PHP as FPM Application served by Apache" on version 7.2 and it worked perfectly
- I tried creating a new domain to test if there was an issue with PHP 7.4 or nginx. I created a domain with the exact same settings as example.com and it worked : /opt/plesk/php/7.4/etc/php-fpm.d/test.com.conf showed "pm.max_children = 200"

=> Do I need to re-create my domain example.com ?
I'd rather not do that to prevent any issue with my current users.
Any way to reset something ?

Many thanks !