Referencing sub-classed (child) Blueprints Causes errors and crashes

This is a bit tricky, and I’ve had a hard time replicating it, but I’m now spending more time trying to work around this issue than working on my game and my tasks are starting to slip behind schedule!

Referencing derived blueprint classes compiles correctly and runs as expected, yet causes the editor to crash when loading levels or attempting to edit blueprints after saving, exiting and restarting the editor.

Version 4.2.1
Blueprint Project (No C++, Content Only)

What seems to be the issue is referencing and spawning sub-classed pawns (and, sometimes, but not always other sub-classed blueprints)

I have a Pawn class that I’ve sub-classed to create variations. These sub-classes change default values only (However, the bug happens even if the values are not changed). Other classes such as power-ups, HUD, etc. refer to the Pawn by the parent class (Generally by casting) to access variables, events and functions. All of this is pretty typical game design.

When I make reference to these classes in other classes, the game/blueprints compile just fine while running the editor and everything works as expected.

However, once I save the compiled blueprints, exit the editor and reopen the project, referencing these blueprints in any way causes an instant crash.

Here’s video of this happening:

Strange workaround thingy: This isn’t exactly a workaround as it’s unreliable but most of the time, I can load a blueprint that’s isn’t part of the reference tree described above. It takes a few seconds, seemingly recompiling the blueprints, opens the selected BP. then, i can open and edit the problematic blueprints. I mention this as it may shed some light into why this seems to work when I first reference the child classes, but causes a crash when the editor is reopened.

I have noticed similar behaviour in the last 2 days. It has only happened a few times, but reading this post makes me think it may not be a coincidence. I have been trying out using child blueprint actors, and have been messing about with references/transforms, etc… Over the last few days I have crashed out completely to a system reboot three times. There are no error messages in the system log and I don’t even get a BSOD! I have been using UE4 each time. I wonder if it is connected to the behaviour that you have noticed?

4.2.1 here too, running on windows 7 x64.

Same issue for me as well…my Child Blueprint class has no info in it’s details panel…

Also side note for me (wondering if it happens with anyone else…) if I run the editor for awhile then use the “find variable references” it’ll crash…so heads up if you use that make sure to save first…

There’s definitely some major issues in UE4 using blueprints to make a larger game/systems.
They work phenomenally until your systems get complex and then not only do they fail, they fail spectacularly and don’t offer much in the way of way to fix 'em. this issue has basically halted development of my game and it makes me so sad :frowning:
I’m about to watch all the C++ tutorials tonight and move everything over to code so that we can move forward :confused: At least it’s going to look good on my resume! :smiley:

Please, Epic, please help us fix this!

This has continued to happen over the last day, with 5 more crashes to reboot and no error messages in sys logs. After seeing that there have been a few posts in this hub recently regarding child blueprints AND structs I, sadly, have now pulled apart my blueprint components and removed the structs as well. My last load of UE4 seemed to work OK with these changes, so I hope this was the problem and that they can get this fixed this up soon!

I’ve moved this to the Bug Reports section since there’s some collaboration of this issue being greater than something in my particular project.

I’m working on replicating the issue in a clean project, but I’m having trouble nailing down the exact combination of things to make it happen. I’ll keep this thread updated as I explore the issue.

Just to update, I have had no further issues since deleting the struct and breaking out my child BP’s. I’m not 100% sure which was the issue, but I strongly suspect it was the struct. I have read another bug report detailing an issue about corrupted structs ([here])1. When I attempted to resolve this, I only deleted the struct that I had been recently working on - another, older struct I left running (as it was too integrated and I was doing initial troubleshooting after reading the other post), and everything has been fine since.

And I was sooo looking forward to structs too - let’s hope their stability improves over the next few updates.


Thank you for your report. We were not able to investigate this on the engine version you reported, but there have been many version changes to UE4 since this question was first posted. With a new version of the Engine comes new fixes and it is possible that this issue has changed or may no longer occur. Due to timetable of when this issue was first posted, we are marking this post as resolved for tracking purposes.

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