Not Monitoring Text Messages

Good morning,

I have two children whose smartphones are being monitored with Norton Family. I have set up message monitoring on both, but only one (A) is actually allowing me to see messages. I know that the other (C) is sending messages, because I can see them coming through on A's phone.

I double checked their Norton Family settings side by side, and they seem to be the same.

What else can I do?

Thanks