Good day, I have the same issue with menus, and Im using version 2.6 for Darker Nodes and UE4 4.25.4 . also if I do FixElements it just says it Failed to Save for all elements!
Update: I think I know what is happening, your Plugin don’t like Multiple Projects Open while using Darker Nodes, Some things get Broken.
Closing both Projects and opening just one allowed me to fix Elements and get the menu Fixed!