Another two years later, I found this happening to some meshes in 5.4 (animals from the asset store). Sorry for the revivify but this is the only discussion I’ve found on the subject at all. Setting the LOD CPU Access property on the sk meshes didn’t resolve the error. Neither did recompiles etc. However, I noticed the one mesh I use my Niagara system as the Preview Mesh was working okay. So going back into the Niagara system, in the Initialize Mesh Reproduction Sprite, I set the Preview Mesh to one of the non-working meshes and a CPU Error warning appeared in the details editor with a Fix Now button. Clicking that to clear the error, and repeating the process for the other meshes, allowed them all to work. I don’t know what the Fix Now button is changing on the mesh other than the CPU Access bool that was already set, but give it a try if your stuck.