Note: despite not technically being a regression due to being a bug with a later introduced feature, this bug will stop you from being able to do things that you can do in 7.x.x due to the fact that there is no stage limitation on subgraphs in that version. The first version this bug reproduces in is 10.4.0.

Repro steps:
1. Copy the attached shadergraph and subgraph into your project
2. Open the shadergraph
3. Try to plug the first output of the subgraph (NormalOut) into the vertex position stack node

Expected result: it lets you (This will work! Because when the shader compiles it will optimize out the part of the function that is not used in that instance. Doing this in 7.x.x where stage limitations on subgraphs doesn't exist yet will result in a shadergraph that compiles.)
Actual result: it blocks you from connecting that output because of the ddx in the subgraph that is connected to the other output