When you open the project, you might see that some nodes can't be loaded. For instance, some merge conflicts can cause that. At this point, all possible nodes are loaded to the project, but when you open it, the following warning is shown:
In the project you'll see the nodes with these icons:
This is a Broken node. It can not be created manually, it is shown if some node can't be loaded into the project. A Broken node has the following context menu:
Show in explorer. Open the folder with the node in the file manager.
There is no tab for a Broken node to be opened in, and it can't have any child nodes. The main purpose of this node type is to help you fix the error.