I have the same problem with the 0.9k version. At some point, fps starts to lag inexorably with drawdowns every second from 60+ to 11-12, and this problem was in poorly optimized versions up to 0.8.2 Changing settings does not help, even if you reduce the quality to low, it's just a crappy optimization. At the same time, I returned to version 0.9, and it started normally on medium and high settings. And yes, light consumes a lot more fps than shadows or post-processing, which is a big problem, because the more settings they shove into the graphics, the worse the game is optimized in the end.
Also flashes of lightning during the storm completely crushing the game, I don't know what is this, but it's annoying incredibly. I hate this.