we’re experiencing an issue with UE 5.6 with Control Rigs and LODs. The repro steps are broken down in the thread, and you can see a video with the issue on the Mannequin.
Essentially if a character has a control rig that loads dynamically his skeleton hierarchy in the Construction Event by using the Import Skeleton node, it will now glitch in game when switching between LODs.
Depending on the complexity of the system being applied (procedural LookAt, FeetIK, etc.), the issue can be spotted more severly. The video attached shows it with some procedural LookAt on top.
[Image Removed]
The issue doesn’t seem to occur in 5.5 as we have extensively used this method to build systems compatible with different skeletons’ hierarchies and was working appropriately.
Create a control rig with a Construction Event and an Import Skeleton. Don’t load any hierarchy as the goal would be to spawn/load at runtime the skeleton from the character that is using this control rig (imagine being used in a system where a base ABP is shared among different characters with different skeletons and therefore we load on Construction event so to build a universal reusable system).
Spawn a hierarchy of Ctrls from you spine and head joints.
In the Forward Solve, Apply a Constraint (for example, a Rotation Constraint) where you Child is the bone and the Parent is the control. Tick Mantain offset if controls are in a different space than the joints.
In the Skeletal mesh:
Create LODs for your character, making evident changes in the triangle count and removing some bones, ideally not those being used in the control rig system
Add an AnimBP to load the control rig and make sure to tick the option in the control rig node to Set Initial Transforms from Mesh.
Play in the level while showing a.VisualizeLODs 1, and observe the skeletal mesh glitching when swapping LOD.
I’ve confirmed that this LOD glitch does not occur in UE 5.5 but is present in UE 5.6 and later versions, including Main P4 (CL 45016667). I have submitted a JIRA report so that the engine team can investigate and address it.
Please note that Epic ultimately determines whether the issue will be made publicly accessible and the process may take a few days. The tracking link might not work immediately.
I’ll go ahead and close the case, but feel free to reply if you have anything else to add.