In order to analyse any issue, it might be useful to check the corresponding output files.
At the moment you will find all necessary files generated by >%WEB_PLOT%> at the following location:
C:\arcgisserver\directories\arcgisjobs\vertigis_utilities\vertigis_printingtools_gpserver

Printing - output folder
.aprx
This dynamically generated .aprx contains all necessary data an information, which is used for creating the plot output.
.log
The generated logfile in order to find out, at which point the problem occured.
Note: At the moment it's not possible to make any customization, likke defining the location, setting any loglevels or generally activate or deactivate, the logfile. At the moment it will be automatically activated with all different kind of loglevels on.
The generated output file.
Note: In order to generate qualified support requests of VertiGIS Printing please first have a look at these files and in case include them into your request.