If you are trying to use a backup, or another Cron job that fails, it may be because there is a queue of job and one failed. This is an error message shown from our backup plugin – updraft plus.
You can install this free plugin show below to view the Cron jobs awaiting. You can even use this to delete entries you do not want. If you see the same item repeated, then you know your system is having a problem with executing the items in the queue.
If there is a long list, or you prefer a quicker way than Adding the plugin, you can delete them all from your database with one line of MySql
UPDATE wp_options SET option_value = '' WHERE option_name = 'cron';
They may not all disappear because some plugins and WordPress Core will be adding items that they expect to be there. However, this should be a handful, not dozens.
Once you have brought the system back in line, you need to take actions to make sure that the problems do not happen again. This is either because the Cron job does not run correctly, or a particular Cron action fails to run.
You can use your cpanel to see the activity for your cpu and cron. If a plugin is ‘running a muck’, you may find this here.