I ended up resolving the issue on my own.
Viewing post in Shora Lighting & Shadow System (RPG Maker MV/MZ Plugin) comments
I have the same issue. How did you fix it?
*edit: I fixed it that way: enter in the plug in manager -> right click on '-ShoraLightning-' -> Edit -> double click on [Lights: Default] -> Double click on Image [.png] -> click on the bar before 'img/lights/' -> select 'default' (the light png example image) -> click 'ok' and that's it!