Hi,
If you use the free plugin "WP Crontrol", then you can view a list of scheduled tasks registered with the WordPress scheduler.
However, I suspect you'll only find one UpdraftPlus one there (or rather, one for files, one for DB), and that the true cause is that either the webserver or database server is extremely overloaded - which can cause database updates to be lost, or delayed, which in turn causes WordPress's built-in scheduler (which UD relies upon) to repeat events.
David