As part of the backupnode startup, the backupnode scripts calls daliadmin to retrieve the Thor group, if Dali is down or coming up, it will issue 'Failed to connect to Dali' etc.. Due to the way the backupnode script is written, these errors will be captured and redirected into the 'slaves' file, corrupting it in the process.
If Dali comes up at this point, the slaves file output will complete, but be proceeded with the error messages and cause problems for the rest of the script.