Recently encountered backup issue on one of the primary site server and backup never ends stuck at “info:starting asynchronous do snapshotset… ” though sms_site_backup service running and never(did not monitored for too longtime) ends until you stop it manually.
Below is the snapshot captured when error occurred.
Why does it hangs over there ? what are the causes ?
Tried Restarting the sms_site_backup service but doesn’t fix the issue and log hangs with above message.
So decided to restart the sccm server (caution in production server) and check if the sccm services are running or not like sms agent host and sms_executive.
Now start sms_site_backup_service and monitor the logs ,you will positive answer from logs 
.