Comtrade's latest HYCU Nutanix backup product version has a fix for the VM stun problem.
An ESX virtual machine is quiesced (stunned) when a backup is taken. This can cause IO latency problems as IO requests come in to the "stunned" VM, are stored, and then consolidated into the stunned VM when the backup completes and stunning stops.
The delays can be long enough to cause application timeouts and even server failover. Comtrade says it can solve this issue because it uses Nutanix storage-level snapshots instead of the usual hypervisor-level snapshots.