iPhoneX doesn't alert me when receiving text messages from a particular contact My iPhone X won't alert me when I receive a text from one particular contact. This is happening with only one contact. It vibrates, but there is no notification, and when I open the Messages app, the message that was sent to me appears as if it has already been read. I do not have do not disturb on, and have tried to set a special text tone for this one contact.
I see that you said you do not have "Do not disturb" but there is also a contact specific setting "Hide alerts."

Go to Messages> select the contact that for which you don't receive the notification and make sure the "Hide alerts" toggle is not enabled.