Only a single menu item is listed, not a generic menu of items. The menu item fails when selected because NoiseBase is an abstract type.
It took me about 5 hours of FlowCanvas source debugging to figure out that <T> is required in the [Name] attribute. This is undocumented and also not very robust.
I am sorry for the inconvenience. The [Name] attribute was mostly made as a mean to completely override the name of the class if required and is really not mandatory. If you just remove the [Name] attribute, the node will correctly show up in the editor as the rest of the generic nodes, with it’s class name “NoiseNode (T)”.
With that said, I just improved the [Name] attribute usage for the next version, so that it’s more convenient when used with generic nodes and it does not require “” to be manually added anymore.