Because beta versions of applications and iOS are significantly less reliable and bug-prone than final releases, joining the iOS beta program isn't a smart idea, especially if you're having serious problems. We recommend reverting to version 11.4 and seeing if it makes a difference. Here's how you can do it:

1. Open the Settings application.
2. Select General.
3. Select Profile & Device Management from the drop-down menu. Go to Profiles and choose it.
4. When the iOS Beta Software Profile shows, tap it.
5. Then tap Delete Profile to get rid of the Beta Software Profile.

1. Use a USB cable to connect your iPhone 8 to iTunes on your computer.
2. Then immediately push and release the Volume Up button.
3. Quickly press and release the Volume Down button.
4. Then, until you see the recovery-mode screen, press and hold the Side button.
5. Select Restore when iTunes offers you the choice to restore or upgrade your iOS device. This will allow you to return the device to its original factory settings.
6. To activate your device, sign in with your Apple ID from iTunes after it's finished.
7. Then, using a previous backup, restore all of your data.
8. Continue by pressing the Enter key.
9. Check for the problem by restarting your iPhone 8.