@PichouPichou, I spoke with @Deltakosh about it and there was at some point a discussion to include lighting information in a reflection probe, but there has not been any movement on that work as a feature because there are some outstanding questions about how we would approach it. I would not rely on that as a solution at this point as it could give you some hiccups. You are correct that you can limit the reflection probe to render once, but there is still no IBL in it.
What you are seeing in the playground you sent over is incorrect behavior being masked by the helmet asset. As most of the asset is very reflective, it’s easy to miss the fact that the harmonics are off in the hoses. If you feed the reflectionProbe texture into the reflectionTexture as you are here, you are missing all of the harmonics information that PBR needs to render correctly. To quickly show this, I replaced the asset with the one I use for testing roughness and you can see that there are no roughness values being calculated.
The playground on the right has only IBL from a DDS texture in the scene and you can see roughness values from 0.0 to 1.0 at an interval of 0.1 per sphere. While it is not in the correct orientation in you playground, you can see that the metallic spheres are all roughness 0 and the dieletric materials are just rendering incorrectly as black spheres rather than white.
In your case, if you want local reflections, you still need both IBL for the PBR materials and a reflection probe for reflections. But if you are just trying to create IBL for your PBR materials, you can’t use a reflection probe at this time due to the harmonics not being calculated.