Client agents stuck running tasks

NS Version 7.1 SP1

We sometimes notice some of our client PCs get stuck running tasks and any subsequent tasks refuse to run.  See the attached screenshot for how this appears in the client PC task history.  Looking at the same tasks on the server - they all fail with "The task timed out on the Task Server while waiting for the agent to pick it up"

This means we cannot run tasks on these computers.  The solution so far is to re-deploy them.

What causes this problem and is there a easier workaround other than re-deploying the PCs to solve it?