I’ve just opened a baseplate - no modifications to Lighting or anything besides creating a new transparent part - and this weird shadow appears. It happens on any transparent material. I tried it on another one without a baseplate and the same thing happened. It also only happens if there is a part nearly under it (this part is 1 stud tall and 1 stud above the baseplate), but it still happens if it is still a few studs above the other part.
Here is an image:
Hmm, have you tried turning off all of your plugins temporarily (if you have any)? They can do funky things sometimes. If that works, it’s time to play the fun game of guess and check as to which plugin it is. That’s honestly the only thing I can think of given the nature of this wacky occurrence. Let me know if this works.
I’ve seen this too. I’m pretty sure it’s something to do with the fog or atmosphere properties in lighting. Not sure though.
I found this with a quick search:
Unfortunately there wasn’t a solution posted.
Does the CastShadow fix it.? Try disabling it?
It does fix it, but the shadow contributes to the lighting. I wonder if there’s a way to keep both?
Disabling all my plugins didn’t fix it.
Disabling all of the atmosphere fog didn’t fix it either.
If it helps, Roblox now has two lighting styles. You can’t pick Classic or Future like you used to be able to do, you can only pick Realistic and Soft. Neither of them fixed the issue, though.
I am also currently dealing with the same issue with yours, did some research, cant find solution too, although since I don’t need the shadow, for me I will just disable castshadow
edit : Ive noticed that the circle shadow occurs as you zoom in your perspective and disappears when you zoom out or if you yourself is far away from the light
ok I will change my statement, castshadow does not fix it either 
I found the solution! Go to your workspace explorer, under workspace > lighting folder > go to its properties and uncheck “PrioritizeLightingQuality”. This will make the circle shadow in lightings disappear.
At first Ive noticed the circular shadow doesnt seem to be actually a shadow: anything in the circle will look the same as the highest quality appearance of the light, the same as what it looks like in roblox studio before you hit play or simulate your game. Therefore i digged into anything related to rendering and found that. This should fix your issue because i also fixed mine this way. Have fun programming and wishing you success in your game:)
