One contact doesn’t sound when texting yet others do??

Open the Messages app. Locate the thread with the name of the person that you are referring to. Is there an icon, on the right , that looks like a BELL with a SLASH through it? If YES, then that indicates that the sound notifications for that person have been silenced. If this is the case, then you can TOUCH that Message thread and then SLIDE it to the LEFT. This will display options to Silence Sound (BELL) and Delete thread (TRASH CAN). Tap on the Sound option (BELL) and that will reinstate the sound notifications for this one person.

Axel F.