This used to work for me with my normal struct (not nested in another struct, no data tables, just a struct) whenever I changed something and everything breaks. So, since I always look this up and find this post when I have a similar error, this is what works for me:
- Change the struct
- Attempt to play the game so that the editor compiles all blueprints
- Hit cancel on the “several blueprints encountered errors” window
- Go to the blueprints that encountered errors and disconnect the red wires to whatever you changed
- Attempt to play the game again so that the editor compiles all blueprints
- Save all
Now you should be able to close the editor and re-open it again to continue working with your modified struct.