We have an IoT company and we shipped more than 10.000 products around the world. We have some of our customers (around 5%) that cannot connect their product to MQTT.
Our infrastructure is really easy. Once the user send WiFi credentials to our product via bluetooth, it connects to the WiFi and sends a request to our server. The server respond with the certificates to connect to the MQTT broker (AWS IoT Core), as soon as the product has this certificates it connects to MQTT broker and starts the communication but this connection never happen.
The problem is that we cannot replicate this kind of problem in any way. We tried to buy the same routers of our customers but everything works fine.
The port used by the device is the 8883 and the authentication uses X.509 client certificates.
Do you have any idea of which could be the issue?
Thank you so much!