Hi Rhyce – There is a few potential reasons for this happening and ill break them down quickly so you can give them a go and hopefully alleviate the issue.
 
First up is that this could potentially be your skylight not updating fast enough and causing your scene to be lit by that – heading to the trueSKY skylight and lowering the update frequency and amortization (along with checking the “update all faces and all mips” option for good measure)
 
Alternatively this could be due to your moon lighting, we simulate moon light into the scene, so if your moon is especially large it will take control of your directional sunlight once the sun has set, and cast light dependent on this. I will say looking at your image however i doubt it is this due to no shadows being cast from the sunlight on the rock on the beach.
 
Finally it could be the starlight option we have added – some users mentioned that their night scenes were too dark, so we added in a star light option to the trueSKY actor, which does a set brightness directional light pointed straight down and doesn’t cast shadows – Finding this setting within the trueSKY actor and lowering its intensity or turning it off might also help fix this up.
 
Hope one of these fixes the issue for you – if not let me know and ill give it some investigation. And as always any other issues feel free to reach out.
 
Chris @ simul