For a long time, probably since the game first released, any object that uses the 'Cabinet' shader has some displeasing issues with the way that light works on it.
Despite the name of the shader, this issue isn't specific to kitchen cabinets, but to wall objects that are meant to tile together seamlessly (and they use the 'Cabinet' shader to achieve that). This can be the curtain rods from the Desert Luxe Kit, modular shelves from Dream Home Decorator and the Book Nook Kit, or the pegboard from the Comfy Gamer Kit as some examples.
I've personally understood that the purpose of this shader is to allow for light to work seamlessly across wall objects that are meant to tile together (which is something that the 'Phong' shader - used by the majority of objects in the game - does not allow for). The floor counterpart to this is the 'Counters' shader, which is used for tileable floor objects such as kitchen counters and modular sofas.
Tileable floor and wall objects having their own specific shaders could be because of the difference in the way occluder shadows behave on them. Some CC creators actually use 'Counters' as a shader for their kitchen cabinets (because of how bad the 'Cabinet' shader is), but I guess because of the way occluders behave on a 'Counters' shader, they end up having horrible shadows cast on them when placed above a fridge. To fix this, players have to get a mod that straight up removes occluders from appliances.
In the end, right now the 'Cabinet' shader does somewhat do its job (most of the time a row of cabinets on a straight wall in an evenly lit room look seamless) but it's not great, especially when comparing it to the 'Counters' shader.
Here's a few examples showcasing the difference:
Objects using the 'Cabinet' shader have this incredibly stark lighting going on for no apparent reason, especially when comparing it to how normal the lighting is on objects using a 'Counters' or a 'Phong' shader. I'll add that the above examples were taken with the object directly in front of the light source. When placing the modular shelves or cabinets more to the side of where the light comes, it looks more natural.
There also apparent tiling issues on corners, epecially when multiple light sources are involved:
All of those cabinets have the same swatch. The lighting just isn't smooth, even though it should be.
Building kitchens and using modular shelves have a bit of a sour taste to it, because of how bugged the lighting seems to be on objects using the 'Cabinet' shader.
All pictures were taken in a game with the highest graphical settings and without mods or custom visual changes.
