A7672E with ESP32 connects to APN, but doesn't connect to MQTT Broker

[lg007]

[x] I have read the Troubleshooting section of the ReadMe

What type of issues is this?

[ ] Request to support a new module

[ ] Bug or problem compiling the library
[x] Bug or issue with library functionality (ie, sending data over TCP/IP)
[ ] Question or request for help

What are you working with?

Modem: A7672E
Main processor board: ESP32 devkit
TinyGSM version: 12.0
Code: The MQTTClient example code (with own APN set and with the modification that is needed for the ESP32)

Scenario, steps to reproduce

Just try the MQTTClient example with the modification that is needed for the ESP32:
SerialAT.begin(115200, SERIAL_8N1, 16, 17, false) // the modem is connected to pins 16 and 17

Expected result

I expect being able to connect to the MQTT Broker

Actual result

Connection to the network is OK (the LED of the modem blinks fast). The connection to the MQTT Broker fails.

Debug and AT command log

If I reproduce the same circuit with another module (a SIM800L), it works and connects to the MQTT Broker (with the same APN). Of course I change the #define for the modem that I use.

[lg007]

An interesting fact: if I change the MODEM define to the following:
#define TINY_GSM_MODEM_SIM7600

instead of this:
#define TINY_GSM_MODEM_A7672X
then everything works!

Has anyone any idea?

[SRGDamia1]

Hmm. A lot of the SIMCom modules are very similar and have more than one way to connect. I wonder if it's something to do with the "application" stack vs the TCP stack. That's why there are two versions of the SIM7000.