Hi David,
From looking at the code that error/message is occurring because it is not finding any pertinent repository monitor records in the [RepositoryMonitorStates] It is looking for any records with branches named default or master... This is leading me to believe that there is a configuration issue that doesn't generate an exception when monitoring or no changes were found. Additional logging might be something worth looking into. Without any additional information it would be hard to determine on our end.
Thanks,
Jason