UE4 Crashing Whilst Working on Multiple Monitors

I am writing this as a solution for anyone who may be experiencing the same issues I did, and to see if anyone else has any theories that could trump my own.

This issue plagued me for weeks with me knowing nothing about what was actually causing it and making me not want to use Unreal Engine because it didn’t make sense as to why it was crashing.
This was an issue which I could not use the bug report feature because the bug report was always blank, and my system was totally bricked from the crash of Unreal Engine.

I will give some context as to my system specs, what I use Unreal for and what happens at the time of the crash. As I say I believe I have figured out what causes the issue but maybe someone with some more experience could either confirm or debunk my theory and perhaps explain as to why this occurs.

My System Specs:

  • i7-9700k

  • RTX 2080

  • 64GB RAM

  • Samsung 28” 4K Monitor (3840 x 2160 @ 60Hz HDMI)

  • Alienware 240Hz Monitor (1920 x 1080 @ 240Hz HDMI)

  • Wacom Cintiq Pro 24.5” (3840 x 2160 @ 60Hz DisplayPort)

  • Unreal Engine 4.26.1

  • Unreal Engine 4.25.4

  • Windows 10

I am letting you know the specs because I don’t see the power of my PC being an issue as it is only 2 years old.

Usage

I started learning Game Development at the start of 2021, I am an Artist by trade so can-do design and modelling and the rest of it I just needed to learn code and to use Unreal Engine. I took a Skillshare course and Codecademy’s C++ course before starting on GameDev.tv’s Learn to Code with Unreal Engine course and I am relatively confident now after a month – obviously still got stuff to understand and develop to become really good but I am competent at least.

Reason I point this out is because of the use of pointers within C++ which can cause a lot of errors and fatal crashes from accessing memory which the software doesn’t have permission to access. So I do know about stuff like that, but I was confident about my null pointer checks that this wasn’t what was going on.

An Example Crash

I was working on a 2.5D platformer (3D World, 2D Character) this is still very early development so style, design and everything is still needed to be worked out. Just working on the core mechanics at this stage.

The project is a C++ project made from the blank template. There are a few custom classes most notably the PaperCharacterBase class which houses movement mechanics such as double jump and wall jump.

Editing on my main 4k monitor is no issue, but when I drag the blueprint window across to my secondary monitor which is (1080p) then the whole system crashes and defuncts my whole PC where no input does anything (this can either happen immediately or a minute after Unreal Crashes).

The Problem

The problem is when switching to a secondary monitor Unreal Engine crashes and eventually takes my whole system with it.

Troubleshooting

Wacom Tablet: Someone mentioned on a forum that a Wacom Tablet can cause Unreal Engine to crash. So, I turned off my Wacom, and it did not stop the issue occurring.

Null Pointers in C++ Code: Having learnt C++ with Skillshare and Codecademy as well as learning it with Unreal Engine through GameDev.tv I do Null Pointer checks in my code, something like: if (AActor* Actor == nullptr) { return;}. As this stops the code running any further if a null pointer is found, hence stopping the software crashing. If you put in a UE Log message as well it helps with debugging as to where the null pointer is. I double checked my null pointer checks but once again, this did not fix the issue.

Antivirus Software: This could potentially be an issue, so if you’re running antivirus add you project and Unreal Engine to the exceptions, but again I don’t believe this was the sole reason for it crashing as Unreal was running and executing perfectly fine. If you’re having the exact same issue as me then I would suggest this is not the problem you’re facing.

C++ Code: Another theory I had was that it was something I kept doing that wasn’t pointer related within C++, so I tested out to see whether the issue occurred with a solely blueprint project. Lo and behold it did. So this was a bit of a relief that I wasn’t just awful at C++. This kind of ruled out any problem with C++, so C++ is not the issue.

Monitors: I tested to see whether dragging the blueprint onto my Wacom Display crashed unreal, no it did not. I then drag it onto my Alienware monitor and bingo. Dragging an Unreal Editor window onto my Alienware monitor seems to be the reason it crashes. See the solution I posted to answer this problem for my explanation.

Any Ideas?

I do believe I have homed in on what the issue is, however, if you believe I am wrong please let me know. Do you have any solutions to this problem, or do you know why it occurs? I would be grateful to hear what your thoughts are on this issue.

Solution

Different Resolution monitors cause unreal to crash. Either stop using the different resolution monitor or artificially change the resolution of the monitor using software (Nvidia have a software for GeForce cards to change the resolution of the monitor, but the issue is they warn it voids monitor warranties so I chose not to use the monitor).

Explanation of Theory

The input HDMI and the Display Port does not seem to be the issue. The Wacom runs off display port and the Samsung runs off HDMI but moving UE windows between the two does not cause a crash.

The refresh is also not the issue. I set the Alienware down to 60Hz in line with the other two monitors and it did not fix the issue, the editor still crashed and crashed my whole PC with it when moving editor windows.

The only other difference between the monitors is resolution. The Wacom and the Samsung are both 4K screens (3840 x 2160), the Alienware is the one which is (1920 x 1080) and this is the one where if I drag a window onto it then it crashes. So, my best theory is the resolution difference is the issue. What does confuse me though is the fact that I am sure I used the Alienware as a second monitor for Unreal without this being an issue back at the beginning of January 2021 but now every time it just crashes regardless of the engine version. So, if you know more about this than me please get in touch by leaving a comment! Thanks

Please make sure you plug both/all monitors into the same video card, not the onboard video port of your motherboard. I can corroborate your symptoms, which were driving me nuts until I found this post!

I too tried the OPs test of setting both monitors at the same resolution, and as nutty as it sounds can attest that it did indeed work! I have no idea why that would be the case, maybe some nutty optimisation behind the scenes… I have no idea.

It would be great if Epic could fix this issue - must be more than just us experiencing this.

To replicate, create a brand new project, undock and move the output log to a screen other than the one UE was using for the graphics interface, and at a different resolution. If it doesn’t hang during the drag, when the output log is maximised UE would hang. (I just repeated the process for a sanity check, as I agree it is insane, but yes, it hangs straight away when maximised on a different video card, on a different resolution.)

It’s been a loooong day so apologies for rambling, or if this post makes no sense. I’m a professional software engineer and very experienced with multi-headed apps, having worked on the university’s driving simulator - 8 screens that one, but at the end of a very long week waffle is inevitable.

Lastly, thank you to the OP for posting. I did a google and it is not a common problem, presumably as most people only have one video card, or don’t use the onboard graphics at all. If this does not tie in with your symptoms I apologise, it’s so nice to have a reason for the crash that at this stage I’m just grateful to have a soulmate.

(Sorry for reviving a year old post, but trust me. If anyone else is in this position the post is worth finding, even if it simply makes you check where your monitors are actually plugged in, not where you assume they are… as in my case.)

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