Thanks. I turned it off. Truncated the table. The site is flying again.
Sounds reasonable. I'll keep an eye on it.
Cpanel upgrade a few weeks back updated backup retention after export to s3 so I filled a hard drive. It's been chaos ever since. The cron probably failed that night and hasn't run since. My backups were taking longer than 24 hours so it never finished.
I know I'm out of date and planning to update soon but a feature request could be a better alert around cron failures via email instead of just the cp.