@Shankar KUSUMA Thanks for reaching out to us. Please follow the general troubleshooting guidance - https://video2.skills-academy.com/en-us/azure/migrate/troubleshoot-appliance-discovery#discovered-vms-not-in-portal
Select Refresh on the Servers tab. This should show the count of the discovered servers in Azure Migrate: Server Assessment and Azure Migrate: Server Migration.
If this doesn't work and you're discovering VMware servers:
Verify that the vCenter account you specified has permissions set correctly, with access to at least one VM.
Azure Migrate can't discover VMware VMs if the vCenter account has access granted at vCenter VM folder level. Learn more about scoping discovery.
Also, refer to the MSDN forum link - https://social.msdn.microsoft.com/Forums/en-US/7ad4617b-085b-4120-804e-ef37eea3d154/endless-discovery-is-in-progress?forum=AzureMigrate
Hope this helps. Feel free to write back to us if issue persist!