Check the following (Remember that a cycle behavior is similar to that of a filter).
Clean up invalid variable formulas. Ensure the formulas behind your variables are valid
Clean up duplicate variables. Each variable must have a unique name in order to prevent issues for NPrinting reporting
Clean up unused variables. In past cases we found thousands of unused variables were parsed and caused the _FAILED_ report output
Make sure that the dimension(s) in your report 'cycle' are all valid.
Simply create a new, simple report with a single valid chart and cycle the report with the dimension that results in "FAILED" report output name. Then create report task with this report and execute the task.
If the task works with no other filters in use, there could be some kind of filter/cycle conflict
Check that the dimensions you are trying to access in a report 'cycle' and report 'filter' do not conflict.
Removing the conflicting filter (same filter used in the cycle) may resolve the issue.
NPrinting Upgrade may be required:
Check if the issue still persists in NPrinting November 2020 (or higher version). If you are on an older version please do first an according upgrade on a test environment and test if this solves the reported issue (as the upgrade might solve the defect "OP-9394" which caused the error "ERROR: System.InvalidOperationException: Collection was modified; enumeration operation may not execute.")