Hello @Selvaraj ,
Do you still see the status of VMSS as Updating ?
Check the instances status ( validate if they are in Running State)
Try to STOP & START the VMSS .
If the VMSS is in failed state , try to check the activity logs from "Activity Log" section from the same VMSS view in Azure Portal - it will show you the reason for the failure.
Regards,
Shiva.