Snowed Grass side and Layered snow have different brightness both in Day/Night, Night but near powerful light source. here I attach a few more screenshots, taken in Bedrock edition:

Day time

Night time

Night time near light source.

Clearly is a Bug as: It looks totally off, especially in game play near snowy Mountains, seeing different brightness destroys connectivity of textures, which is obviously a Bad thing.
Here I attach an screenshot of How It's supposed to Look:
 
image taken in Java edition, Layered snow & Snow block perfectly connect to Snow grass side without disturbance, unlike bedrock edition.
I also believe this bug didn't exist some version before 1.17