Hardware Ray Tracing Causing Black Flashing in 5.1

I have this random black pulsing or flashing in UE5.1 I cannot get rid of, except if I turn off “use hardware ray tracing when available.” Then instantly it goes away. The consequence is, I lose my shadows in my foliage and other places. I have no idea how to fix this. I removed and re-installed the 5.1 Engine and that worked for about 20 minutes but now its back. I’ve turned off thousands of objects, even foliage and my landscape and still it persists. It’s definitely a rendering issue with ray tracing but no idea how to make it go away. Would love any help or suggestions.

Finally got it fixed! For anyone else who has this issue I will mark this as solved.
Turned out the flashing was being caused by some Niagara particle systems I am using. I could select the Niagara systems and turn off “visible in ray tracing,” and that would make the flashing go away. A more systemic fix was to go into the Niagara systems and I found that if I selected GPU Compute for the simulation instead of CPU the flashing goes away and I can leave on the “visible in ray tracing” option. Glad to have it fixed but what a headache.

Black flashing is back. All Niagara systems are turned off. So I have no idea what to do now. If anyone has a suggestion that will solve the issue I’m prepared to offer a $200 reward. I’ve spent a lot of time on this and its holding me back in my work. I’m working solo so the only help I’ve got is online. I thought it was the Niagara systems but I’ve changed them all over to GPU Simulation and even turned them all off and the issue persists.

Hey there @MichaelRev1412! This looks a bit like a Temporal AA issue I’ve seen before. So let’s run through a couple of things and see what we can do!

Could you try sliding into your project settings and adjust the AA method? Just kind of play with each of them (including none) in the meantime to see if they have any effect.

if it does have an effect, this could be an old bug with TAA history cropping back up.

If not, it could be distance field issues (but I doubt it considering the nature of the flashing). To test that, go to your primary lights and turn off distance field shadows and see if it stops. If so, it could be trace issues.

Lastly if on Nvidia, are you running studio drivers? Game Ready drivers are great, but the studio drivers usually help the editor have far more stability especially with RTX.

Thanks for the tips. I’ve tried all those previously except running the game drivers. I’ve stuck with studio drivers for the stability purposes. I did however find that I had an extra Niagara system that got missed when I was changing the simulation method to GPU. When I switched all the Niagara systems to GPU simulation the flashing went away immediately and has stayed away. So that’s what the black flashing was related to. Why? I have absolutely no idea. Maybe the Niagara systems using the CPU to calculate was conflicting with the GPU in some way? In any case, that’s how I solved it – turning all the Niagara systems to GPU simulation instead of CPU.

That is quite odd, were those particles just billboards or were they meshes? This might point us in the direction when I finish making the report. Amazing work!

They were not meshes, but Niagara particle systems. I used the ribbon renderer. I would love to know how to animate a cylindrical type mesh along a spline but dont even know if that’s possible?
Hope that helps!

That’s excellent information! Usually if we get too far off topic on a thread we tend to make a new one, but this is a pretty straight forward one I believe. You just need to move a cylinder down a spline?

Disclaimer: One or more of these links are unaffiliated with Epic Games. Epic Games is not liable for anything that may occur outside of this Unreal Engine domain. Please exercise your best judgment when following links outside of the forums.

Here’s a couple of tutorials for moving objects down splines.

Making a mesh move along a spline (using timelines):

Thanks. Glad the information is of some help!
As for the mesh on a spline, I’d like to be able to extrude or extend it along a spline. Like when one draws a circle around a word or something. I want it to have the same effect but in 3D. That is what I am using the Niagara particles systems for with the ribbon renderer above. I have the ribbon renderer setup as a tube shape with 12 faces, so its more circular like a straw. And then I just animate it around text in UE as if drawing a circle around a word or some text. The Niagara systems are getting me by right now, but I’d like to use a mesh if possible because I can make it emissive and make the colors glow. See video example below made in blender. Maybe there is a way to do that with Niagara systems too but I haven’t found it yet. Thanks for the help!

You absolutely can! Theoretically you could use a spline mesh, and move the end point along your trace, and dynamically generate/manipulate the spline points with it. Will take a bit of math to get right without brute forcing it and making many spline points (which is totally feasible if it’s going to disappear shortly after but if you make a bunch it could be really taxing). Splines or spline meshes could work, straight up splines will need more setup but will be able to have more control, but spline meshes work out of the box.

Disclaimer: One or more of these links are unaffiliated with Epic Games. Epic Games is not liable for anything that may occur outside of this Unreal Engine domain. Please exercise your best judgment when following links outside of the forums.

I’ve got a couple resources that could help with that!

Basics of spline manipulation in BP:

Longform training on splines and spline mesh:

I have a similar issue with no NIagara in the scene, only some meshes and the flick is onyl in low-light areas. Any suggestion?