We are currently running Magento 2.4.3-p1 with MSI and are having issues with ghost orders. Note that we also had the same issues previously when we were running 2.3.4, so it doesn't appear to be as a result of the upgrade. We run few extensions beyond popular payment gateways, MailChimp, SMTP etc, so I don't think there's much going on outside of vanilla Magento at checkout.
We've had some limited customer feedback suggesting they are receiving an error stating the order was unsuccessful and to try again. Some customers have done so, resulting in multiple payments, others have reached out.
This doesn't happen consistently, nor are there any errors in the logs at the time of these issues. Interestingly, we are seeing the affected customer carts in the quote table, and also their payment transaction is in the quote_payment table. However, for whatever reason, these are not being converted into orders, and there's no trace in the sales_order table.
Has anybody seen anything like this, or got any suggestions as to where we can look? Unfortunately it's really inconsistent - we can have no issues for an entire week, then 2 or 3 in a single afternoon, so it's difficult to pin down.