Hi,
If you have set cron job on twice daily and there in no user visited site then cron job not run on that day. because WordPress trigger cron file on user/admin view.
Also
Might be cron job setting not updated properly in option table.
logging into phpMyAdmin and UPDATE wp_options SET backup option_value to monthly
OR clear all cron job and set setting again.
Please check following url for more information.
https://codex.wordpress.org/Function_Reference/wp_clear_scheduled_hook
https://hackguard.com/blog/clear-cron-jobs-wordpress
Bro the code is broken. It does not work.
You set it to run on any setting it only takes hourly backups.
So I think you need to look at the code and fix it.