Sorry it's taken me a while to get back to this, been a bit swamped. I've attached a simple scene that shows my issue and a few screen grabs. In this example an area light for the sphere only is set to ID 8. The toroid then has ID 8 deflected, so the light does not affect it. There's a second area light with no adjustments, that should affect all items. If I set both area lights to general usability of 0 then the sphere light only shows a reflection on the sphere, which is as expected. However if it is set to 1 then the reflection on the sphere is still the same but we get an additional black reflection on the toroid. Both items are 100% metallic.
Edited to add the file, apparently, LXO files are not allowed on this forum.