It may be just that you needed to wait a bit longer (a few minutes to finish scanning of certain devices).
Another way of dealing with this issue could be setting the max thread run-time to 30 or 60 seconds in the config file:
<maxruntime>60</maxruntime>
This will make the app attempt to gracefully finish scanning any devices that are slow to respond; and if that fails, forcibly finish the scanning of those by interrupting any pending network I/O operations after double length of the timeout.
You can also launch the app without the
/hide switch to see which devices prevent the scanner from finishing the scan.