When you realise that updates havent been downloading as intended, one of the first places to look is have a look is at your Auto Deployment Rules.
Go to Software Library and choose Automatic Deployment Rules
In the main window you should be able to see the error code and why your Auto Deployment Rule hasnt run. The error in this example is 0x87d20415, as per the below image.
The issue is that SCCM has a hard coded limit on the number of updates (1000) that can be downloaded by an Automatic Deployment Rule. The best place to start to investigate that this is the case, is to check the ruleengine.log, located install directory – Microsoft Configuration Manager – Logs – ruleengine.log.
Looking at the file with cmtrace, you should be able to easily identify that this is in fact the issue. (Issue highlighted in yellow)
You can see that the ADR has hit the 1000 update limits as highlighted in yellow above.
To overcome this issue, you need to set the date revised or released to the last month. This way, SCCM will only check for updates released in this period. To do this, right click on your Automatic Deployment Rule and click properties. Go to the Software Updates tab, and choose Date Released or Revised, and set this for a more suitable time frame (1 month should suffice, but this does depend on your Update deployment schedule)
Once you have changed this range, go to your Automatic Deployment Rule, and choose Run Now.
Once this has been completed, check the Ruleengine.log once again, and you should hopefully see that the updates are now in fact downloading and the dreaded error, Auto Deployment Rule Error 0x87d20415 has disappeared.
If you are having general SCCM Deployment issues, see here how to solve them