If an internal error interrupts execution _cohort and _control_cohort are not cleaned up. We should add them to the variables that are cleaned up after errors.
Summary: In this isse we added _cohort and _control_cohort to the variables that need to be cleaned up in case of a mid-execution error.
Thread continues in #211
If an internal error interrupts execution _cohort and _control_cohort are not cleaned up. We should add them to the variables that are cleaned up after errors.