Hi Karl -
Is there any other backup software installed onto the system?
Is the machine being managed by SSR MS 2013 console?
Is it possible that the base backup is still in progress when the incremental is scheduled to kick off? The log file should have an information message about this if this is the case. You can also look at the C:\ProgramData\Symantec\SYMANTEC SYSTEM RECOVERY\LOGS\Symantec System Recovery.log.txt file and see if there is anything therein that might indicate what was going on when the scheduled backup should have kicked off.
Try modifying the job to run either 5 minutes ahead, or 5 minutes behind your current setting. For example, if it is scheduled to run at 12:30, change it to 12:35.