You know your project better than anyone.
I can only go based off what you tell me and what I see.
Just keep in mind that all actors, by default, are set to “0”. I’m sure you’re already aware of this, but I still do think there’s a conflict going on, and that conflict is causing spikes in lighting complexity. (You should keep the complexity view on WHILE you move the camera around and adjust settings so you can see what’s actually going on with the lights.)
I’m unclear if you’ve tested each scenario one-by-one, because how you’re using Light Channels is very… unique. So, turn them all off, set them all to “0”, and then individually enable each light, systematically, testing if when/if you get the artifact.