I am not terribly advanced, but could offer some questions that might help you find more information!
What makes you say that there are ad-hoc tasks that are not running? "Course backup ad hoc task pending: 6" just means that the automated course backup process started, and assigned 6 courses to be backed up by the ad-hoc task handler. It then immediately writes that in an email (it does not wait for the ad-hoc tasks to finish, successfully or otherwise), so it does not mean they necessarily failed.
When you go to Site administration > Reports > Backups, are there any Errors, Unfinished, Pending, etc in the Status column? Or is everything either OK or Skipped?
Next - I am wondering if the cron error is related to your course backups, or something else. Where did that cron report come from? Moodle Scheduled task logs? Server cron logs? I could be mistaken, but "cronerrorclionly" sounds like your cron job might not be getting run at all (which means a lot of things on your site might not be working).
Here is a page in the Moodle docs with the same error message: https://docs.moodle.org/310/en/Cron#The_web_based_Moodle_cron_command
When you go to Site administration > Reports > Status, are there any warnings/messages there? Do you have command-line access to your server? Are you on managed hosting?
Sorry I can't provide any solutions! I hope those questions help you get moving in the right direction, at least.