So I just arrived at Vulcanus, got attacked a few times by Big Demolishers (in the starting area) even before I mined any tungsten ore, and when checking Rampant settings, I noticed Vulcanus attacks should only be enabled above 25% Evolution. Which I shouldn't have reached yet.

But when I checked Vulcanus' Evolution, I was already at 1.000. I didn't kill any Demolisher, and landed for the first time 30 minutes ago. How is that possible?

There's clearly a bug, I used the console to set the evolution to 0, and a couple minutes later it was 1.000 again.

Yes, it's a bug. Or rather, an error accidentally added right before the release

Unfortunately, for unknown reasons, documentation for the Factorio commands is currently unavailable on the mod portal, so a fix won't be released until tomorrow.