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4.9 crashes randomly when compiling a big BP or clicking Play after doing so


I ported one of my projects from 4.8 to 4.9 and it made my work filled with crashes. 4.9 crashes randomly (but very, very often) when compiling a big BP or clicking Play after doing so. I work on such BP, with a lot of variables and functions and haven't got such problems earlier with it (other, much smaller projects in 4.9 don't cause something like this). Now every time I try to compile it or PIE I can only hope it won't crush. Saving beforehand helps to preserve my work, but it's very frustrating, as you can probably imagine. ;) I don't know how to help you narrow the problem in any other way than sending you my BP, but I must do it with a private message. Just let me know where and who should be a recipient.

PS I've already sent a few reports by the interface that shows up after crash. Today tried with 4.9.1 but nothing changed.

Product Version: UE 4.9
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asked Sep 15 '15 at 08:35 PM in Bug Reports

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avatar image Ben Halliday STAFF Sep 15 '15 at 08:56 PM

Hi Nox_A15,

Thanks for submitting the report through Crash Reporter. Next time this crash occurs, please copy the Machine ID before hitting Send, and post it in a comment here so we can look it up in our system. Additionally, please zip and attach the logs from the project's \Saved\Logs folder. That'll give us a place to start investigating, and we may ask for the BP later. Thanks!

avatar image Nox_A15 Sep 16 '15 at 12:47 AM

Hello Ben,

No problem, here is the ID and the Logs folder:



PS This time it crashed after hitting Play and worked quite long without crashing in the BP editor. But that's probably in the logs.

avatar image Ben Halliday STAFF Sep 16 '15 at 03:11 PM

Thanks Nox! Looks like we have a couple of other crash reports with similar call stacks, and a larger number with the same error message. I'm going to enter a bug report for these, but it would be extremely helpful to have a copy of a project in which this occurs. If you don't mind, please zip up and upload your project someplace like Dropbox or Google Drive and send me a link via PM on the forums:


And let me know which BP in particular seems to be causing the crash on compile or PIE. That way I can give the devs something to reproduce the issue with.


avatar image Nox_A15 Sep 17 '15 at 06:53 PM

I've just sent you the link and forgot to mention about placement of the BP, so there are two messages in total. :) Look for "Test Project for 4.9 BP Crashes".

avatar image Allar Sep 16 '15 at 03:18 PM

I though this was normal behavior xD

Kidding aside, in my personal experience this "IsA" BP crash issue is exacerbated when working with Widget Blueprints and their classes. Maybe that's only a perceived pattern, but every time I hit compile in a Widget Blueprint I hold my breath anticipating the crash.

avatar image Ben Halliday STAFF Sep 16 '15 at 03:33 PM

We have another bug open that has that same basic error involving widgets, I believe. Different call stack, though, so I'm not sure.

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Hey Nox,

Thanks for the project! I was able to reproduce the crash in 4.9.1, but I can't seem to locate the specific reason for the crash. I've created a bug report and linked your project for the devs to look at (UE-21255). I suspect it's related to another similar call stack which we also have reported (UE-20750), so hopefully we'll find a solution soon. I will update this post when I see any progress.

I unfortunately do not have a workaround at this time, but as I have time I'll attempt to find one for you so you can submit to marketplace. I'll post here if I find one.

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answered Sep 18 '15 at 06:50 PM

avatar image Dan.OConnor STAFF Jan 12 '16 at 08:44 PM

I was not able to reproduce the crash in 4.11. The most likely fix is this commit.

Thanks for sharing your project with us, it's a huge help.

avatar image Nox_A15 Jan 18 '16 at 10:29 PM

No problem, glad it helped! :) Thank you for looking into it! I will test it out when the fix will make it to the next Preview build.

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