Summary
I observe rapid disappearance and reappearance of non-Nanite instanced foliage while Groom is enabled. Parts of pine trunks, pine leaves and some small ground twigs are affected. Grass, shrubs and ordinary placed static meshes appear stable. Even different sections of the same tree can behave differently. With a stationary camera, individual sections flicker frequently, and a larger group of foliage can briefly disappear at roughly 5–8 second intervals.
Setting r.HairStrands.Enable 0 immediately stops the observed flicker; restoring it to 1 brings the flicker back. Disabling RBF on the affected Groom also suppresses it, but breaks the intended hair deformation/placement. I need to keep Groom working correctly, so disabling hair or RBF is not a usable solution.
Environment: Unreal Engine 5.8.2 (Launcher, CL 56702186), Windows 11 25H2 build 26200.9457, NVIDIA GeForce RTX 5070 Ti Laptop GPU, driver 616.92 (32.0.16.1692), D3D12 / SM6. Nanite is disabled; NVIDIA is the selected rendering adapter. Changing temporal-AA and fullscreen/windowed modes did not resolve the issue. I have not tested 5.8.3.
What Type of Bug are you experiencing?
Rendering (Graphics / Niagara)
Steps to Reproduce
I have not yet isolated a minimal standalone reproduction. These steps describe the affected scene, not a claim that every scene with foliage and Groom reproduces it.
- Run the affected scene with non-Nanite instanced foliage and a skeletal character with a bound Groom. Keep Groom and RBF enabled.
- Let startup settle, then hold the camera still for at least 30 seconds.
- Observe parts of trunks and leaves rapidly disappearing and reappearing.
- Set r.HairStrands.Enable 0 and observe that the flicker stops. Restore it to 1 and observe the flicker returning.
- As a separate comparison, disable RBF on the affected Groom. The foliage flicker is suppressed, but hair deformation/placement becomes incorrect. Restore RBF.
Expected Result
All foliage sections should remain consistently visible while Groom renders and deforms correctly.
Observed Result
Trunk and leaf sections rapidly disappear and reappear, sometimes across a large group of trees. Disabling Hair Strands suppresses the observed artifact, but also removes the hair.
Affects Versions
5.8
Platform(s)
Windows
The symptoms seem similar to UE-360482: https://issues.unrealengine.com/issue/UE-360482 . I have not confirmed the same underlying mechanism with a GPU capture.
Could this be related to UE-360482? Is there a renderer fix or supported workaround that preserves Groom and foliage appearance, including any relevant change in 5.8.3? Please advise what minimal reproduction data or GPU capture would help isolate it.