When connecting to my realm following the update, all of the light-emitting blocks in nearby chunks ceased to emit light. Reloading the chunks doesn't solve it. Mobs are able to spawn right next to torches leading me to believe it is server based, not client. I cannot seem to reproduce the bug in another location, it seems to be localized in the nearby chunks where I initially connected. The location does not have sky access which may be part of it. Updating the lighting by placing and breaking a new light source seems to temporarily fix the area. But the error comes back upon reconnecting.