Magento – Magento 2.3.1 Error on checkout getAdditionalInformation()

I've migrated an old webshop from 1.9 to 2.3.0 and then upgraded to 2.3.1. And I've come across a problem that I can't quite find out why it is happening. There are about 300 products migrated into Magento 2.3, they all have the price of zero. When I try to use the onepage checkout, I get an error at the final step and it stops there.

I've got multiple extensions installed:
– Forced Login
– Disable Register
– Infortis (To edit theme)

Example when I try to checkout:

I get a 500 error on the path: /index.php/rest/nl/V1/carts/mine/payment-information

With a report saying this error:

Fatal Error: 'Uncaught Error: Call to a member function
getAdditionalInformation() on null in
domain.nl/public_html/vendor/magento/module-sales/Model/OrderRepository.php:172\nStack
trace:\n#0
domain.nl/public_html/vendor/magento/module-sales/Model/OrderRepository.php(134): Magento\Sales\Model\OrderRepository->setPaymentAdditionalInfo(Object(Magento\Sales\Model\Order\Interceptor))\n#1
domain.nl/public_html/vendor/magento/framework/Interception/Interceptor.php(58):
Magento\Sales\Model\OrderRepository->get('668')\n#2
domain.nl/public_html/vendor/magento/framework/Interception/Interceptor.php(138): Magento\Sales\Model\OrderRepository\Interceptor->___callParent('get',
Array)\n#3
domain.nl/public_html/vendor/magento/framework/Interception/Interceptor.php(153): Magento\Sales\Model\OrderRepository\Interceptor->Mage' in
'domain.nl/public_html/vendor/magento/module-sales/Model/OrderRepository.php'
on line 172

I can't find anything about it online and I have no idea how to fix this or what's causing it.

Some other insight I'd be thankful for, if you need any other information, please do not hesitate to ask!

Thank you!