Ever since I started using Blueprints that derive from other Blueprints, the UE4 Editor crashes nearly every time I compile the Blueprint.
I’ve attached the crash report data. If you need the project, I can get it to you with repro steps.
I really hope this has already been fixed in 4.9 because working with these frequent crashes is very difficult.
I don’t know how to read the output log, that’s Unreal’s business but I’ve had the same problem before. I remember that I did something stupid and there was a bug related to animations.
I’m not really sure anymore but I think mine crashed due to the fact that my parent called a function directly that was located in the child. Of course that doesn’t work because a parent does not see it’s child, it’s child only sees the parent.
So make sure you did not do something like that 
Hi sranck,
I’m taking a look at the crash reports we’ve gotten from you (thanks for submitting them!), and it looks like the majority do indeed involve an Anim Blueprint, though perhaps its source is simply a BP derived from Pawn or something. Please check the suggestion Serellyn made above and see if there are any calls to a function in a child from its parent, and let us know if there is.
Otherwise, this crash does not look familiar, and I can’t find another in our database for it. Would you mind uploading the project somewhere and getting me a download link? You can send it privately via PM on the forums, if you’d prefer:
https://forums.unrealengine.com/member.php?32-Ben-Halliday
Thanks!
Thanks for the replies. I don’t quite understand what you’d like me to check, but I did PM Ben a link to the crashing project and provided repro steps.
Hi sranck,
I tested each Case in both your original project and a new, “clean,” project I created with 4.8.3’s Third Person Blueprint Template, migrating your agents assets over. The results are as follows:
(A) CRASH 1
(B) CRASH 2
This tells us that there’s some conflict or something is corrupted in your master project, but if you *migrate your agent assets to a clean Third Person Blueprint project this will take care of the crashes.
It’s disconcerting that a UE4 project can suddenly become corrupted to the point where it’s unusable, and the only solutions are to either migrate everything to a clean project, or revert to an earlier backup. I’m hoping you can provide my corrupted project to one of your programmers to take a look at and perhaps discover what exactly became corrupted. Perhaps it would provide enough information to track down the bug and fix it in a future release. This seems like a very important bug to fix.
Unfortunately, due to vast quantities of assets in your project, we simply do not have the resources to debug your project to isolate why the crash is occurring. For instance, you have included the entire Kite demo, among numerous other asset packs, and your project only appears to be referencing the grass from that pack.
By testing your assets with your repro steps in a new project, we have isolated the cause to be not that of the engine itself. So saying the project has become “corrupt” is a general statement as there is likely some reference to an asset the engine cannot find. This may be the sole cause of the crash or in additon to the errors generated by the blend nodes discussed in your previous thread. (ie the “conflict.”)
The next steps I’d recommend to debug on your own are to:
Missing assets (“reference to an asset the engine cannot find”) should never cause the UE4 Editor to crash & become permanently unusable. Missing assets usually produce a warning message, so I assume that whatever’s causing the Editor to crash is a bug in the engine itself.
The crashes literally started happening the instant I introduced another layer to my Character BP and Anim BP, and started adding functionality to the new layers, which involved renaming some functions. From that point on, compiling my Character BP began crashing the Editor, and my Anim BP became so unstable that I couldn’t even delete a node without the Editor crashing. This really appears to be a bug in the engine itself.
The fact that my testbed project has the entire Kite demo in it shouldn’t make it any more difficult for a programmer to track down a crash. Visual Studio will just trigger an exception, and from there the programmer can take a look at what caused the crash.
I would think that your engine programmers would want to know that there’s a defect in the engine that can cause the Editor to become permanently unstable, and would be glad to have a project where the crashes can be reproduced so that they can track down the cause and fix the bug.
We are interested in getting to the bottom of this whether it’s a bug with the engine or resolving the issue so you can continue your project. You wrote,“The crashes literally started happening the instant I introduced another layer to my Character BP and Anim BP, and started adding functionality to the new layers, which involved renaming some functions.”
Please answer with as much detailed information as possible.
Thanks.
Thanks, Steve. FWIW, we are a paying UE4 support client, so if you’d prefer that I post this on UDN, please let me know.
-1-
Before things started crashing, AgentAR2_CharacterBlueprint’s parent class was Character. I created a new BP called Agent_CharacterBP, whose parent class was Character, and then reparented AgentAR2_CharacterBlueprint to Agent_CharacterBP. After doing the reparenting, I relocated some functions and probably some variables from AgentAR2_CharacterBlueprint to Agent_CharacterBP. I don’t recall which. I also introduced virtual functions such as GetAgentWeaponBP in Agent_CharacterBP, but where the implementation is actually in AgentAR2_CharacterBlueprint.
Also, AgentAR2_AnimBP’s parent class was originally AnimInstance. I renamed AgentAR2_AnimBP to Agent_AnimBP (because it already had a lot of functionality that I needed to keep), and then created a new BP called AgentAR2_AnimBP and parented it to Agent_AnimBP. The idea was that AgentAR2_AnimBP could then use its own unique set of animations by specifying those animation names as variables (the K_* variables found in the “Anims” section of Agent_AnimBP).
-2-
Sure, if that’s the case then there’s likely a bug in the engine’s renaming functionality. Recall, however, that the crash occurs when I compile Agent_CharacterBP or AgentAR2_CharacterBlueprint, and not when the game is run. If the engine is trying to call a stale function, wouldn’t that occur when the game is running as opposed to the BP being compiled?
One side note is that when I compiled my BP and the editor would crash, when I then relaunched the editor, the BP had already been compiled successfully and I wouldn’t have to recompile it again (until I made another change, of course). The game ran fine.
-3-
No, the project was initially started with 4.8.
Thanks, Steve. FWIW, we are a paying UE4 support client, so if you’d prefer that I post this on UDN, please let me know.
Hi sranck,
Please post this issue in UDN. AnswerHub is a hub for community driven support.
Thanks,
Sean
Thanks Sean. Done.