Hi Andy,
Those must be zombie processes; if they were actually doing anything, then later UD runs would detect them. (UD checks the file modification times of the zips its working on).
To switch to a different zip engine that doesn't use external zip binaries, add this to your wp-config.php:
define('UPDRAFTPLUS_NO_BINZIP', true);
For stopping regularly scheduled backups, choose "Manual" from the list of options for backup schedules on the UD settings page.
David