It is important to know just how much space is "all available space". The agents will use a buffer on disk if they cannot reach the gateway, and it can be a couple of gigs (100MB is the default, I think)
In some cases, customers have an "application" disk that has only a few hundred megabytes free. If the agent couldn't reach the gateway (or the gateway is overloaded and couldn't handle all the incoming connections) AND you had the agent installed on a disk with very little free space, this could be expected behavior.
The solutions are to either configure the agent to have a smaller buffer (not great, because someone can always use enough of the free space to get it below your threshold and you will fill it), or move the installation to a more appropriately sized disk.
Jim