Changing structs that are being used in UE4 can cause issue later on when trying to package, there are alot of different work arounds and fixes that can work but this is the process I use when changing a struct that is in use.

Edit the struct one variable at a time, for example add or remove or change one variable then if you need to change more restart the steps in this guide.

1. Change the struct, remove, add or change a variable in the struct.
2. Save the struct
3. Play in editor, this forces the engine to recompile any blueprints effected by the changed struct
4. Once the player loads in exit the game
5. Click the Save All button in the content browser
6. Restart the project

I can’t guarantee this will work but its how I change structs and it seams to work for me. Hopefully Epic will address the issues with changing structs soon.