Apple's mobile phone sends text messages in groups. What are the reasons for some receiving and some not receiving?

There is nothing wrong with the mobile phone, but the communication channel is congested. In general, sending five short messages at once will cause communication congestion, resulting in delay in sending or receiving, or even failure to receive. It is suggested to call the manual desk and ask the customer service to help unseal it. Usually, messages can be sent normally within one hour after unsealing, but this phenomenon is inevitable in the case of a large amount of information.