I have noticed some invisible light blocks generating in caves (mostly lush caves for some reason). I am holding a light block in my hand to show that the object emitting light is invisible(and is not a light block i placed), in the image i have also carved out the area that it is in so that it is floating. Its emits about the same light as a Glow Lichen. I believe this may be some kind of glitched Glow Lichen, perhaps glow berry vines and glow lichen are generating on top of each other causing the lichen to disappear.