I was running into this error in UE5.1 Lyra project.
The bug didn’t happen on the regular SK_Mannequin (Manny or Quinn).
In the warning itself it’s saying “either no CPU access is set on the mesh or the data is invalid”
So I checked my new mesh (in my case a frog skeleton mesh) I had needed to enable “Allow CPUAccess” under the LOD Info.
After checkboxing this. It started to work just fine. and no more Niagara warnings
