The double hop issue is the direction I am leaning as well. But, all instances are using the same domain account to run their services, and all three servers are registered as SPNs with the domain account. We are using CNAMEs in DNS to point to the instances, and both of the CNAMEs are registered as SPNs with the domain account as well. The most frustrating thing is why would I be having a double hop issue with one and not with the other?