If an SA say that they are not receiving text messages, but the mobile number is correct in their profile, the most likely scenario is that they have unsubscribed from the mobile texts from your school's designated number.
To rectify this issue the first step is to look up the organizations phone number. You can find this by going to the team module, click on the roster, select the SAs and hit "Send Text" which will open a modal that lists the phone number assigned to your sport.
You will see a yellow bar with the following information "This text message will be sent from (XXX) XXX-XXXX." Above that bar it will also let you know who on your roster has unsubscribed from the number that you have included as a recipient for that text.
Take that number, send it to the student-athlete, and let them know that they will need to text "Start" to that number to resubscribe to team texts.