Hello ,
This issue sounds related to UE-27652, which was an issue with editing struct variables disconnecting pins in blueprints. This issue is reported as fixed in 4.12, so open up a copy of your project there and try it out.
Let me know if that fix works for you, and if not, please recreate the issue in a clean project and provide the repro steps that you used so we can see it on our end.
Have a great day