New to 4.25 was the ability to specify per instance custom float data. It appears to work great for Instanced mesh, but for Hierarchical Instanced Static Mesh the indices are not stable. As the camera moves around the custom data moves to different instances. I have submitted a bug report but I ha…

Adding an answer to say I received an email from Epic in response to a bug report I submitted, stating this has been fixed and should be released in 4.26.