MQTT_KEEP_ALIVE_TIMEOUT in different regions

Hello, we have developed a doorbell product utilizing AWS servers. Currently, the AWS server is located in Tokyo, and it functions properly in Taiwan, Japan, and San Francisco. However, we encounter the MQTT_KEEP_ALIVE_TIMEOUT error when used in Las Vegas. The network connection source for all connections is a phone roaming card, and the devices are identical. The only difference is the location.

Could the device not be successfully connected? Or could it be caused by network instability? We would appreciate any guidance on how to resolve this issue. Thank you.