The night suddenly fell (And I mean suddenly, the sun was setting and then it immediately jumped to the night, with almost no transition in the lightning) and then I spotted this :

Nothing to really add... here is my sky in screenshot.

I tried messing with the graphics settings and found my computer really did not want anything but FASTEST. I borked up myself when I changed resolutions or played with too many settings

Crypto, I've seen that with the tree canopies as well. The time of day doesn't matter, I think. Basically, the canopy in the near field is made transparent if there's nothing behind it. Might be similar to glass/water reflections, which don't always match the true environmental conditions? For example, get close to any shiny window at night, you'll probably see the day reflected (definitely true of dome building near the park entrance).