Hi, I had originally posted this in the MegaLights feedback thread and they advised me to drop it in here instead. In a nutshell, been experimenting with 5.5 and if I have Substrate enabled and then enable MegaLights I get a consistent crash mentioning SubstrateGlobalUniformParameters != nullptr || !IsSubstrateEnabled(). If I disable MegaLights again the level works as expected.
(full error is in in the link below)