Looking at the Support case notes, they think it is possibly related to the NIC drivers, because the communication between the Primary and the Backup servers gets backed up to the point of causing a switch when you publish from the new server. The case is still open waiting some feedback from your reseller, who is still working with Support to resolve the issue...
So, the main thing to look for is the difference between the old server and the new one, especially at the point of communication between the two (looks like you have a dedicated NIC for the communication between the switchover pair?)