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.