src/Web/Sessions/Session.php
protected function freeze()
    {
        if ($this->getIsActive()) {
            if (isset($this->data)) {
                $this->frozenSessionData = $this->data;
            }
            //$this->close();
            if (Reaction::isDebug()) {
                Reaction::info('Session frozen');
            }
        }
    }
protected function freeze()
    {
        if ($this->getIsActive()) {
            if (isset($this->data)) {
                $this->frozenSessionData = $this->data;
            }
            //$this->close();
            if (Reaction::isDebug()) {
                Reaction::info('Session frozen');
            }
        }
    }
If session is started it's not possible to edit session ini settings. In PHP7.2+ it throws exception.
This function saves session data to temporary variable and stop session.