Assignment submissions are now loading successfully in Crocodoc, if they are Crocodoc-supported file types (see our Canvas Guide at https://community.canvaslms.com/docs/DOC-2959 for more information).
Upon initial investigation, it seemed that the errors we were seeing on the back-end for Crocodoc files in Canvas were coming from the Crocodoc service itself. In working with Crocodoc (Box), they confirmed that their services were functioning appropriately. This led our engineers to verifying our settings once again. Upon doing so, they found a global required setting that had been misconfigured. Upon repairing the configuration, Crocodoc file preview has returned to normal functionality.