Dangling reroute nodes have no source of value. For that reason, such reroute nodes are ignored by geometry nodes. Other node systems still have to handle this case more explicitly. To users this behavior generally makes sense, but it's also not completely obvious. Now, there is a new tooltip when hovering over dangling reroute nodes that mentions how those work. Pull Request: https://projects.blender.org/blender/blender/pulls/120851