It seems like the display resolution on the Galaxy S7 could default to fullHD (1920 x 1080) after the Android Nougat update. Now, don't worry, you will still have access to QHD (2560 x 1440) resolution, but you'll have to change it manually. This report comes from SamMobile, they've noticed that this happened on the Galaxy S7 after they've manually updated one of their devices to Android Nougat. Now, it is possible this happens only after manually updating the device for some reason, or perhaps their device is an exception for some reason, but it's certainly something to keep in mind if you're planning to update your Galaxy S7 sometime soon.
If you happen to update your device, and want to switch back to the QHD (2560 x 1440) resolution, simply navigate to Settings -> Display Menu, and you'll see the option to switch it back to QHD (2560 x 1440). The source tried to revert it back to QHD (2560 x 1440), and they were successful, all you have to do is restart the device after you flip the switch, and that's it. This could be a bug in Android Nougat, which is not that big of a deal considering you can easily switch the resolution back, but still, some people might not even notice that they're using a fullHD (1920 x 1080) display all of the sudden. As many of you know, the option to switch the resolution on Samsung's devices appeared on the Galaxy Note 7 first, and is now available on both the Galaxy S7 and Galaxy S7 Edge as part of the Android Nougat update. We do not know if a similar bug is present in the Android Nougat build for the Galaxy S7 Edge, but it is possible.
Samsung had started rolling out Android Nougat to the Galaxy S7 and Galaxy S7 Edge quite recently, after thoroughly testing it for the past couple of months through the beta channel. Android Nougat is bringing a ton of new features and options to the Galaxy S7 and Galaxy S7 Edge, including a more robust notification shade, better battery life, slightly changed user interface, and so on, these are only some examples.