FASTPANEL - mpm prefork - AH00161 server reached MaxRequestWorkers setting, consider raising the MaxRequestWorkers setting

# tail -f /var/log/apache2/error.log
[mpm_prefork:error] [pid 24955] AH00161: server reached MaxRequestWorkers setting, consider raising the MaxRequestWorkers setting
[mpm_prefork:notice] [pid 24955] AH00169: caught SIGTERM, shutting down

Ошибка только для MPM PREFORK, но поднять MaxRequestWorkers можно для всех MPM до 1024:

# vi /etc/apache2/mods-available/mpm_prefork.conf
# vi /etc/apache2/mods-available/mpm_worker.conf
# vi /etc/apache2/mods-available/mpm_event.conf
# vi /etc/apache2/conf.d/99-fastpanel.conf

везде поставить:
MaxRequestWorkers         1024

и перезапустить Apache (Ubuntu 20.04):

# systemctl restart apache2