WSUS : Regularly some different clients are not reporting

We have about 200 servers and regularly some servers don't report anymore.

However, the Last Contact is from today.

I have a workaround :

1. Stop the Windows Update service
2. Remove the %SystemRoot%\SoftwareDistribution folder
3. Start the Windows Update service

However, I wish to fix the issue instead of constantly using the workaround.

We have only one WSUS server.

Servers which do not report are running Windows 2008 or windows 2012.