I think the two line bodies are not connected at their common point - in design modeler go t o the two parts/lines select them on the tree, right mouse button click and choose form new part (multi-body part_ - that will share the topology at the common vertex.
See how the form new part tool is used:
https://www.youtube.com/watch?v=oQcuJSUfCZ4
If it is in spaceclaim use shared topology (search for that and you will find tutorials on that).
Erik
You are navigating away from the AIS Discovery experience