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.
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.