I've been a little surprised as well by the low-light noise/artefacts in nougat. My phone came with nougat though so I can't compare images; everything is brand new though.
To be honest, it looks less like sensor noise to me than image post processing, but it could really be either. I'd like to see some other comparison photos from other users (who know how to keep their lenses clean) under different conditions. It would really suck if LG put out a ****ty update that compromised the video/photo quality of the G5 and it wasn't addressed.
I found 3 factors that affected post processing
1. Battery, if it was low and not in saver mode it could be a bit unpredictable this is something i have seen since 7.x update
2. Location of storage, storing it on a memory card i found would be a factor if you take a series of shots and they still post processing i found sometimes that would affect quality.
As opposed to directly to the phones memory.
If you have a large ammount of programs running in the background do you ever notice a difference? Thats something im looking at.
3. Quality of memory card, as that will jointy go hand in hand with what i just said about number 2.
The main shooter before nougat was very good and beat my G4 in many situations if not all. The quality post nougat update seemed slightly reduced, the shutter reaponse is much slower and will affevt low light situations as well as trying to film anything when moving fast ie. being on a train and filming out the window. It will bounce in and out of focus.
I have contacted LG and they have not given me the time of day for a response. I got the address for one of the senior management of LG UK and he was embarrassed at how he cant even get a response.