Magento – Unable to reindex Product Prices – Foreign Key Constraint Fails

First remove the typo:

$commentModel->setOrderId($order->getId())
                 ->setComment($message)
                 ->save();

Additionally I would suggest to use

$commentModel = Mage::getModel('checkoutcomments/comment')->load($order->getId(), 'order_id');

which would make sure that you are updating the same comment in case your code gets executed twice.

Seems like there is a bug in Magento\SalesRule\Model\Coupon\UpdateCouponUsages, method updateCustomerRuleUsages(). Change it to:

private function updateCustomerRuleUsages(bool $increment, int $ruleId, int $customerId)
{
    /** @var \Magento\SalesRule\Model\Rule\Customer $ruleCustomer */
    $ruleCustomer = $this->ruleCustomerFactory->create();
    $ruleCustomer->loadByCustomerRule($customerId, $ruleId);
    if ($ruleCustomer->getId()) {
        if ($increment || $ruleCustomer->getTimesUsed() > 0) {
            $ruleCustomer->setTimesUsed($ruleCustomer->getTimesUsed() + ($increment ? 1 : -1));
        }
    } elseif ($increment) {
        $ruleCustomer->setCustomerId($customerId)->setRuleId($ruleId)->setTimesUsed(1);
    } else {
        return false;
    }
    $ruleCustomer->save();
}

this is a quick fix