My child is getting this text multiple times per week. It appears as it is addressed from their contact. There are no blocked numbers on this account as I use the whitelist Verizon has on the family plan of 20 numbers to control the flow of contact with my childs devices.
Sounds like someone who isn't on the whitelist is trying to message them and it isn't coming through or your child is messaging someone not on the whitelist. You will need to look at their phone itself to determine the second possibility.
I'm most definitely NOT a VZW employee. If a post answered your question, please mark it as the answer.