This is because you likely have four or more shadowed stationary lights overlapping. Even if it doesn’t look that way, the attenuation radii of the spotlights may still be slightly overlapping. Keep in mind that if you have a stationary directional light that uses shadows it will also count toward that 3 shadowed stationary light limit. So if you have a single directional light, you can have up to 2 stationary spotlights, if you have two directionals, you’ll only have 1 stationary spotlights left to allocate.There’s ways to work around:
Use static and mobility lighting instead:
Static lights are far more performance efficient than both stationary and mobility lights, but they have their drawbacks as well. Being that they render once when you build lighting through lightmass, and will remain unchanged unless they are changed by you in the editor. They also cannot be changed whatsoever during gameplay. And the other major drawback of static lights is that they only affect static objects that can bake lightmaps. So they won’t light moving things like characters and dynamic objects. While mobility lights don’t have that problem, they are extremely performance hungry, so use them as sparingly as possible. Ideally you’d be using all three types in different circumstances and in combination with each other.
Spread Them Out and Clamp Them:
You can either spread them out so they have no overlapping areas, or you can still have them close together but just as long as the areas they light aren’t overlapping.
Only Enable Shadows on Lights That Will have the greatest impact:
You can still have as many stationary lights as you’d like. As long as there isn’t four shadowing sources. You can have 10, 20, or even 100 stationary lights overlapping as long as they have their shadowing disabled and everything will be fine.
Hope this helps.