Parallel processing are enabled and finally we find out this issue are cause by antivirus installed in Hyper-V host recently.
Antivirus live scan cause Hyper-V host take very long time to create snapshot end out all backup are queuing.
We have to disable antivirus live scan in all Hyper-V host as temporary solution.
Anyone know which VEEAM folder/file should exclude from antivirus live scan in Hyper-V host because VEEAM KB (https://www.veeam.com/kb1999
) does not mention it. Or it same as Guess OS and Backup Proxies exclusion?