Hi @obbzy,
Since you did say it has returned, did you report this issue before? If yes, a URL to the ticket would be helpful.
In general, an event fails if the WP cron isn’t able to trigger it on time. By default, the WP cron job relies on visitor traffic or page-load on your website to run, if there isn’t enough traffic it can use the cron events to fail.
Are you using the default WP cron? If yes, could you please try switching to Server Cron and see whether you still face a similar issue or not?
Please check the following for more info:
https://www.hostgator.com/help/article/how-to-replace-wordpress-cron-with-a-real-cron-job
Please do let us know how that goes so that we could check further if needed.
Kind Regards,
Nithin