Concurrent execution gives exception

When the following exception is thrown, the tool stopped execution.

The tool was used with the following parameters:

./libs4ast C:\Users\jbaut\OneDrive\Documents\Uniandes\Maestria\1erSemestre\Pruebas\talleres\taller8-mutants\gnucash-android\app\src\main gnucash ./tmp/mutants . true

But when I set concurrent execution to false, it runs and normally terminate execution.