I could find and fix the problem very easily thanks to your advice!
Hi there, I don’t have much experience in debugging with Visual Studio, but I tried your method. I was successfully able to invoke an error when the editor hit 93% loading. However for the variable Fproperty I couldn’t identify the variable name (see image attached). Is there somewhere else I need to look? Many thanks for your help.
How do I open UE4 with debugger attached?
Hey man, thanks a lot for answering. I managed to do that part but I just cannot go further. Is there a detailed tutorial on it?
Thanks for your answer. Unfortunately couldn’t see it that way. Wonder why, also 4.26, VS 2019. In the end I made a list of every variable I thought I had created since last successful build and started deleting and re-creating those. By dumb luck it was the second one I did.
You should try with engine build from source code. Check this : Building Unreal Engine from Source | Unreal Engine 5.1 Documentation
Building engine from source may takes very long time. In my case, with old hdd, it takes over 10 hours…
And, You should debug with backup copy of your project. If you open and save with differrernt engine version, you may not be able to open the project with launcher version engine.
In Youtube, search with “unreal visual studio debugging” then therer are many tutorials. I have a plan make tutorual about this, But searching will be faster.
Well, the method given by Fury22PL works like a charm. This is definitely a weird Engine bug I had to remove random property and recreate it under a different name.
For people who are wondering how to debug it if they dont have a C++ project.
- Open Epic Games → under UE4 select options → and install Editor Symbols for Debugging.
- Add new C++ class in your blueprint project it will add Visual studio solution.
- Close Editor open the solution and in debugging select → Debug Game Editor → Start Debugging
- The error should appear during loading → just follow call stack as described by Fury.
Thanks Again You’ve saved my ■■■ 
To add to this, if you have notepad++ or the likes, you can do a find in files for “NoneNone” - it helped me track down which blueprint was the one.
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Furry22PL you are my hero.
Took me 5mins after seeing this to find the culprit and I did notice something in my case which may be the cause (even if it is a little weird). The variable was called ‘InGameMenuWidget’ and the variable type was a widget called ‘InGameMenu’. It could be a long short or just coincidence but I wonder if there is some weird internal naming conflict going on in my particular case.
Please can you explain how you did this ?
(Edit) I just found out how
I managed to solve this problem in a very simple way that doesn’t require much technical knowledge, and it only takes a few minutes!
Steps:
- Install and open Notepad++.
- Click Search → Find in Files….
- Search for “NoneNone” (without quotation marks). Make sure that “In all sub-folders” is ticked. Choose your Content directory as directory, and/or the folder where your Blueprints are placed.
- The search procedure should find at least one Blueprint (.uasset) file with a match. Remove all object variables (including e.g., actor references, arrays, maps) in the corresponding Blueprint(s) WITHIN the editor (do not try to change the binary file, it will break things), and replace the variables with fresh ones (they can be of the exact same type). Save your Blueprint.
- Try packaging/building/cooking again. The problem should have been solved. If the problem still persists, try doing the same for all local variables in the matching Blueprint’s different functions.
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I tried this and it couldn’t find anything in my Content directory. Could there be other kinds of corrupted/broken values causing this problem?
Strange. Could the problem be in one of the plugins you use? Maybe search the Plugins folder too. Also try deleting Intermediate and Binaries folders.
This finally worked for me in the end! It’s important to install the UnrealVS Extension as well!
The variable I had to delete and re-implement was also in a Widget Blueprint so that could be a key similarity. It was an Object instance of a C++ class as well.
Yeah the same happened to me , the only way to do it without ripping apart your content is to covert it to a c++ project if it already isn’t then download the engine debugging symbols and follow the instructions above by Furry22pl and Pkulicki
For me the Notepad++ solution worked great. Thanks a lot!