I checked your HTML, it does not contain any "b-sch-dependency" elements which means your client app did not produce any. I am not sure how such a thing can occur. Do you switch dependency feature on and off? If you do, it might so happen that feature gets disabled by accident.
Try listening to some events and log state of the dependencies feature:
Could you please confirm you used latest released version of the Scheduler and latest released version of PDF server?
Scheduler version: 5.6.2
Current server: https://github.com/bryntum/pdf-export-server