Here is an update on what we ended up doing. So we understand that the behavior that we had in 5.6 was actually a bug, since you cannot have IOR 0 physically, so we are not expecting that behavior to come back. However, since this is a big issue for us, we had to find a workaround for it. we realized, if we turn off all lighting channels of the glass meshes, since it wont receive any light from the skylight, it wont reflect the skylight as well, so we directly see the backdrop mesh. However this means that the edges of the glass will appear darker, since there is no light in the scene that can bounce on them. To fix that, we enabled “affect dynamic indirect lighting” on the backdrop mesh, so with emissivity of the already existing hdri texture on the backdrop mesh, we see some minor light bounces on the edges of the glasses. This is a compromise since ideally we don’t want the backdrop to contribute anything to the lighting of the scene, that must be handled by the skylight actor in our lighting plugin, but since typically the backdrop intensity is not that high (otherwise it looks fully white) the difference is negligible. I should mention that we also changed our backdrop material a bit as well and started using Pathtracing ray type swtich to only select the main and indirect specular rays. This way at least rest of the lighting is not affected by the backdrop. However it would be fantastic if in the future we will get the option to separate the reflection rays from GI rays. As of now reflection and GI are tied together which is a big limitation.