The blocking occur intermittent

i have also set sp_configure 'blocked process threshold', 10. .

and when the blocking happened , i try to select other rows in the config table , it return the result .

But when i try to select the row which condition where Getdate() > eff_start_dt and sys_key= 'LAST_USED_LOG_ID' , it will keep loading because these particular key was blocked by the update statement .

But what have cause the blocked for these update statement ? I can see exclusive lock . but there are no other insert or update to the config table except the only one which blocked .