No Text Notifications or Sounds from One Contact
My moms friend had this problem also and we ended up doing searches and found that my mom was listed 4 times in different apps and she deleted them all and put it in again in contacts and it worked. If you go to messages for example and pull down on screen you can search. So it might be entered into several apps. If you pull up more than one then this could help. Just can't hurt to try it.  Or if you go to iCloud.com Mail and Contact settings you can see if there is a rule.