Sometimes it happens. The official updates may cause some troubles to your system. That is why Apple released an update fix to iOS 11. This one goes to those users, who often use FaceTime or make phone calls. If you are one of them, you have to install this update.
In official release notes of 11.0.2 we can see that current update will fix an issue for iPhone 8 and 8 plus, respectively. For example, there is a problem regarding the sound, which may occur during some calls. This 11.0.2 update also can fix a problem with hidden photos. As well as it can fix the process of S/MIME encryption of emails after you are able to open any attachments from your e-mail.
Useful tip: in order to install this update, make sure you made a backup of your iPhone files (The update installation can go wrong, so do not risk). In addition, this one will not be available if you are not connected to Wi-Fi. After the successful connection go to Settings > General > Software Update. Click on the button to proceed. The whole size of the provided fix is 277.3MB.
There is also a problem with downloading. For some users Download and Installation can be not available, so you have to reconnect to your Wi-Fi and repeat the above-mentioned steps.