On some SCCM sites I have seen thousands of errors in despool.log about rejected policy. In some cases these are caused by an non-approved client but on one customer site all clients were approved and there were still 3000-3500 errors in the status every morning.
All the errors came from one single GUID but in the log there was nothing about which Netbios name this client had so the solution was this query:
SELECT
resourceID, netbios_name0, SMS_Unique_Identifier0
FROM
dbo.v_R_System
Select all the results and paste them into Excel or something where you can make a search for the GUID you saw in the log.
I reinstalled the SCCM client on the error-burping server and the log was fine the day after!