On Demand Scanning - Computers stuck on "Waiting" Status

I have set up an On Demand scanning task for a group of computers on our network, set to run nightly. A few of the computer successfully run, but the others seem stuck on “waiting” status so the task never completes before the next nightly scan is scheduled to run.

Any ideas on what could be causing some computers to get stuck in “waiting” and others to run successfully?

We are running AES Administration console (apr2016 build version) on a Windows Server 2012 R2 virtual machine. All client stations are Windows 7. If more information is needed, I’m happy to provide.

Thanks,

CBrandal