The LG G6 rear cameras produces more than average amount of image noise. I am positive that there is an extra sharpening applied to the image, with I think 1px radius. This just makes the noise in the image more prominent. The main cause of that is the small sensor pixels I believe. I've inspected the sample images in GSMArena LG G6 review and you can clearly see that all the images, even the low ISO have noise. For example, that image shot at Montjuïc Castle has a lot of image in the blue sky area. Just magnify the image in 1:1 scale and you can see what I mean. The noise is even visible when you downscale the image. Just for comparison, you can check out the Google Pixel review that GSMArena did and check out the camera samples there, it's a completely different result. The Pixel do due its larger pixels produces images that are almost completely noise free in low ISO. It's even naturally much sharper than the G6 image and looks much better overall.
This is why I am not a fan of camera sensors with small pixels. I don't care about all the marketing and technical explanations that suppose to convince us that even with those small sensors, the camera is capable of taking exception image quality. This is a real limitation that no sensor manufacturer was able to solve. I am not saying that there isn't an improvement, of course there is, and Sony has amazing sensors, but as you can see, even Sony, a leader in the sensor business can't beat physics.
The sensors needs as much light as possible and having larger pixels and a larger light-sensitive area improves the Signal-to-noise ratio. You can see that even with good illumination, the camera still produce noisy images. This is one reason why I love the Google Pixel so much, because it is able to capture really high-quality photos. The LG G6 looks like a joke compared to the Google pixel when you view the image in full 1:1 scale. It's not terrible bad, but you learn to appreciate the Google Pixel camera and understand why it was able to top all the other phones and receive such a high score in DxOMark tests. The LG G6 performs like a good point-and-shoot camera, the Google Pixel performs like a premium large-sensor compact, at least when it comes to low ISO performance.
By the way, I've inspected the EXIF data of the camera sample, that one that was shot in Montjuïc Castle in Barcelona. That test photo was captures at ISO 50 speed rating, at f/1.8 aperture and 1/3167s shutter speed. Although the LG G6 samples were taken with a pre-production model, I just can't see this being solved by a firmware update. This is just a limitation of the sensor. LG had to put two sensors in the camera, and obviously going with a larger sensor for both cameras would have elevated the price.
As for now, I see it as a negative thing about the LG G6 image quality performance. Down-scaled images still look very good with nice colors and sharp details, but even then, for me it's hard to ignore the noise issue. When I look at images with sky, I want the sky to be smooth and clear, not patchy with lots of noise.