Orders Not Created on Magento Store after sales made through amazon and ebay sales channels. – MAGENTO 2 AND M2EPRO SITE

My site used to work fully on the earlier Magento platform using M2EPRO. We have recently upgraded to Magento 2 and M2EPRO for the new platform. We sell through the site and 8 Amazon Channels and 1 Ebay channel. We carry some 2000+ stock items all held with small stock levels. We require accurate synchronised stock control which withdraws stock from sale on ALL channels when any stock item becomes ZERO. Since the site was relaunched under Magento 2 and the appropriate version of M2EPRO we have experienced significant problems where Orders are NOT Created (Magento Order was not created. Reason: Product does not exist.) or where the stock level for an Item does not reduce to ZERO where or not it shows as “OUT OF STOCK”. In these cases the log shows both (QTY has been released. And QTY has been reserved.) I am able to reconcile all orders through the external sales channels and believe the problem is as a result of the Magento 2 and or M2EPRO settings. I want someone who is going to be hands on, identify the issue and resolve it. I can provide full access where required.