Network Topology Mapper 172.19.0.0/1 scan finds node but will not produce map

Network Topology Mapper to scan a large subnet 172.19.0.0/16

Discovery returns 154 nodes found;

Topology processes without an error message but no map created.

The node IP addresses are listed under the shortcuts tab.

I have had several successful scans on similar sized subnet all producing maps.  Anything I am  missing?