Attached video shows this in action, and the title should roughly describe the issue I'm having.

https://www.youtube.com/watch?v=w0FwWfBcTNk

Thanks for your report!

I've actually been thinking off and on about how to solve this issue for a while now. It's a problem that occurs because the searchlight uses an invisible biter to target things since find_entity_in_area() calls are so expensive. When that invisible biter finds a foe just at the edge of the searchlight's range, this behavior you documented occurs.

I still haven't thought of a graceful solution, but I might try implementing an ugly solution that will bother people less.

If it's worth noting, we're also noticing that the searchlights are causing our flamethrower and laser turrets to shoot for about a second then shut off for quite a while? Is this intentional behavior?

You might be running out of power. The searchlights use a lot of it to boost turrets. That's intentional, since the range boost is pretty overpowered otherwise.

I have an outstanding feature request to make the power demand changable as a setting, but haven't gotten to it yet. In the meanwhile, if it's too high you can change it yourself by editing line 72 of sl-defines.lua

We...definitely aren't running out of power with 8 nuclear reactors and 90% of it unused.

I also do believe the electricity usage is perfectly reasonable. It IS very powerful. The laser turrets just won't behave regardless.

Interesting, can you send me your save file by any chance?

https://drive.google.com/file/d/1r7-4kFY1ljaAgIjYfzV7YMM6scs22NHj/view?usp=sharing

This should be it? It has a handful of mods enabled, none are major content. If it's the right world, Nauvis will have a 4x reactor setup over on the left that is very tall (also it was 4 reactors not 8 i am dumb but we're still massively overproducing on power)

Ahh, ok, everything looks fine. Thanks for sending me the save.

I was confused because I was looking for something that looked like the "at maximum range bug", but there's another behavior for balance I failed to mention in this thread:
Turrets that are boosted have a shooting speed penalty of 1 / 30, which causes flamethrowers and lasers to fire intermittently instead of appearing to fire continuously.

I still haven't made a setting to expose this yet, but you can tweak it on line 64 of sl-defines.lua

You can see this laser turret behavior in one of the videos I added to the mod description, where a laser turret is alerted, then shoots only a single pulse in the 8 second long clip below. If you're seeing something completely, different, please let me know and I'll poke around your save file some more.

Oh, I wasn't aware that turrets also had such a significant attack speed penalty while being boosted. I personally believe the heavy power draw is more than enough for balance. I do hope you add a config for that soon.