Task/CounterTask.php
public function flush(ProcessState $state): void
    {
        $modulo = $this->getOption($state, 'flush_every');
        if (0 === $this->counter % $modulo) {
            $state->setSkipped(true);
        } else {
            $state->setOutput($this->counter);
        }
    }
public function flush(ProcessState $state): void
    {
        $modulo = $this->getOption($state, 'flush_every');
        if (0 === $this->counter % $modulo) {
            $state->setSkipped(true);
        } else {
            $state->setOutput($this->counter);
        }
    }
Condition is inversed during flush

@param ProcessState $state