When executing the post-build step "Sonargraph Report Generation & Analysis" the execution starts with this message:
[SEVERE] <SONARGRAPH> Specified Sonargraph system file 'D:\DATA\Jenkins\workspace\D2BS_SEUPLUS_SONAR\ch.raiffeisen.seu.parent\sonargraph\SEUPlus.sonargraph' does not exist!

however the file is present and the user has read privileges.

In the end of the execution another message is present:

[SEVERE] <SONARGRAPH> Failed to process the generated Sonargraph Report

In this case it doesn't matter where in the workspace I set the report directory, it is always generated and it is possible to open both report files.