In SpaceClaim, on the Workbench tab, click Unshare, then click the Share button and type in a 20 mm tolerance value instead of the 0.2 mm tolerance. Send me a screenshot of these points. They should be highlighted with glowing red clouds around each point.
In Mechanical there are ways to turn on the Node ID numbers. I have never needed that in Mechanical, but if you learn how to do that, you will see if there is a single node or duplicate nodes.
If there were duplicate nodes, you could do a Node Merge in Mechanical to join the three beam elements to the same node.