Machines are not reporting SCCM from 30 days

This is a report that check the status of machines and detect if they're not contacting wit SCCM :

select sys.Netbios_Name0,

sys.Client_Type0,

sys.Creation_date0 as 'Creation Date',

sys.Client_Version0,

sys.User_Domain0,

sys.User_Name0,

inst.sms_assigned_sites0 as 'sitecode',

disc.AgentTime as 'Last Discovery date',

hw.LastHWScan as 'Last HW Scan',

sw.LastScanDate as 'Last SW Scan'

from v_R_System sys

left join

(

select ResourceId, MAX(AgentTime) as AgentTime

from v_AgentDiscoveries

group by ResourceId

) as disc on disc.ResourceId = sys.ResourceID

left join v_GS_WORKSTATION_STATUS hw on hw.ResourceID = sys.ResourceID

left join v_GS_LastSoftwareScan sw on sw.ResourceID = sys.ResourceID

left join v_RA_System_SMSAssignedSites inst on inst.resourceid=sys.resourceid

where

disc.AgentTime < getdate()-30

or hw.LastHWScan < getdate()-30

or sw.LastScanDate < getdate()-30

and (sys.Client0 = 1 and sys.Obsolete0=0)

and sys.Name0 in (SELECT Name0

FROM v_r_system

GROUP BY Name0

HAVING COUNT(*) < 2)

order by disc.AgentTime asc