As you can see the bigger campaigns are not going out and are under preparation, which means the data insertion for the 1M+ campaign to the logs table is super slow or it might have stuck during the operation. So you can do the following to get it to work
1. Optimize your logs table by removing the older logs. You can do it by going to Application Settings and set the value for "Delete Campaign Logs After (Days)" to 7.
2. Increase memory_limit in your php.ini file to a better value. I would suggest least should be 2048M for bigger sending. In most of the servers, php.ini is found at /etc/php.ini.
3. Give more RAM to MySQL. You can do it by adding the below line to your my.cnf file. In most of the OS, my.cnf is found at /etc/my.cnf.
innodb_buffer_pool_size = 4G
I would suggest giving half of your RAM to MySQL i.e. if your server has 16GB or RAM, you can allocate 8GB to MySQL.
Make sure to restart apache and MySQL after setting these values.
Make sure to give Mumara several hours after setting the log deletion value in application settings. As the operation will not start instantly. It will be caught up any minute during 24h and it will take additional several hours to delete millions of wasteful records from the table.