Cronjob not working on mautic 3.0.1

It could be a permissions issue: which http engine are you using?

With Apache, try resetting the permissions to www-data and then execute the cron job as www-data, not root.

See the main article here:

You’ll have to change the app/cache and app/logs folders to var/ with v.3.0.0+
sudo -s
chown -R www-data:www-data /var/www/html/mautic
cd /var/www/html/mautic
find . -type d -not -perm 755 -exec chmod 755 {} +
find . -type f -not -perm 644 -exec chmod 644 {} +
chmod -R g+w var/cache/ var/logs/ app/config/
chmod -R g+w media/files/ media/images/ translations/

and then change the crontab file to use ww-data (or assign those tasks to www-data user crontab):
00,15,30,45 * * * * www-data /usr/bin/php /var/www/html/mautic/bin/console mautic:segments:update
05,20,35,50 * * * * www-data /usr/bin/php /var/www/html/mautic/bin/console mautic:campaigns:update
10,25,40,55 * * * * www-data /usr/bin/php /var/www/html/mautic/bin/console mautic:campaigns:trigger

I’d follow this suggestion as well:
It is HIGHLY recommended that you stagger the following required jobs so as to not run the exact same minute.

as seen here: