@Purple Peanut@SamsungAl I can confirm this very same problem happened on my S8, S9, and Note 9. It isn't a huge deal, because I don't use edge lighting (maybe I would if it worked as intended) but I just wanted to chime in to say this is a systemic issue that hasn't been quashed.
I have tried all ways. Edge lighting works when the screen is on but it does not work when the screen is off. I've tried with the setting set to screen off, when the screen is on and always. Very disappointing.