In the UE5.5 MRQ runtime environment, I’ve encountered an issue where, after running my application for around 30 minutes, the entire scene starts flickering during rendering. Here are some key observations from my investigation:
Anti-Aliasing Dependency: The flickering occurs when the Spatial Sample Count is set above 1; if it’s set to 1, the issue does not occur.
Console Variables Workaround: Setting both r.Lumen.ScreenProbeGather.ScreenTraces 0 and r.Lumen.Reflections.ScreenTraces 0 stops the flickering, but this compromise doesn’t yield the desired rendering quality.
Time Dependency: There are no issues within the first 30 minutes of runtime, but the flickering inevitably starts after that.
Irrelevant to Lighting/Post-Processing: The flickering persists even after removing scene lights and post-processing effects.
Has anyone else experienced this issue or found a solution?
Thank you so much for the suggestion regarding Nvidia drivers. Actually, we’ve encountered the flickering issue on several machines. For example, we have systems with 4070 Ti cards running driver versions 560.70 and 566.36, as well as a system with a 3060 running driver version 572.70. and we even have a system with a 3060 running driver version 551.61—which is below 552.22. So, I’m not entirely convinced that the GPU drivers are the sole culprit. I really appreciate your input!!
What does your lumen scene look like? Are things dropping out? So you are saying if you leave a render going for 30mins things will flicker? Are you running low on memory?
Let me walk you through the steps I took to reproduce the issue:
I created an empty project using the “FILM/VIDEO & LEVEL EVENTS” template.
I dragged a few props from StarterContent/Props into the scene and changed the ground material.
Following the simplest implementation outlined in this documentation, I set up a runtime MRQ blueprint and added it to the scene.
In the Movie Pipeline Primary Config, I enabled Anti-Aliasing and set the Spatial Sample Count to 3.
Then, I configured a runtime trigger for the MRQ blueprint’s rendering interface (using the Alt+1 shortcut) and ran the scene.
For the first 30 minutes, the MRQ rendering worked without any issues. However, after 30 - 40 minutes, I started noticing flickering in the rendered output. I monitored the memory usage and didn’t see any signs of a shortage—after all, this is a very simple scene with all settings at their defaults except for the modifications mentioned. Also, when not using MRQ rendering, the scene appears to work perfectly.
If you need any more information, please let me know.
From what I’ve observed, the flickering issue seems to occur only with runtime MRQ. Several colleagues of mine have been using regular MRQ without any reports of this problem.
I’ve done some additional research on this issue and wanted to share an interesting observation. Noticing that the problem appears to be tightly linked to time, I started exploring the relationship between milliseconds and minutes. I discovered that if a signed 32-bit integer is used to represent milliseconds, its maximum value translates to roughly 35.8 minutes.
To test this hypothesis, I ran two experiments using a timer. When I triggered several renders before the game had been running for 35 minutes, no flickering occurred. However, when I started rendering continuously at the 35-minute mark, everything began normally, but after about a minute, flickering started. This seems to support my theory that some part of the code—or perhaps a shader—is using a signed 32-bit integer for milliseconds, and after about 35.8 minutes, it overflows and turns negative.
I only conducted these tests twice, so I’m not entirely certain, but if I get more time, I’ll perform further experiments.
Hey there! Sorry for the delay. I am cirling back around and trying to repro this. I have not been successful. Can you double check me here?
I made a runtime MRQ BP based on the documentation you linked to above.
I made a render config with 3 spatial samples and 1 temporal and linked that in the BP
I hit PIE and let it sit for 40 minutes
When I fire the render I don’t see any flickering.
Hi Shaun,
I placed a chair in the scene and pointed the camera at it, then created a Sequencer. Following the documentation, I made a Blueprint and set up the corresponding trigger event. After the program had been running for fifty minutes, I kicked off the render and noticed the light on the chair flickering. I think you may need to let it render for a bit longer to test this issue.
May I ask which UE version you’re using for your tests? I originally ran into this issue in 5.5.0, and yesterday my colleague tried 5.5.4 but still saw the flicker after about 40 minutes. However, we’ve just tested 5.6.0 and it appears to have resolved the problem—great news for us! Thanks so much for your continued help on this
