AWS connection retry several times

I have a STM32 to use 20210700 FreeRTOS version to connect AWS.
I use LWIP stack on a cellular modem.

I notice almost every time the AWS connection , it will failure and the retry couple of times then success.
May I know the connection backoff retry is an expected behave ?
I notice in rare case, it retry many times but still not able to connect.
any thought how to improve the connection success rate without retry?
any key parameter impact this?
thanks a lot

using_mbedtls_pkcs11 +575 tlsSetup Failed to perform TLS handshake: mbedTLSError=-1, pNoHighLevelMbedTlsCodeStr : ERROR - Generic error.
OtaOverMqtt.c +1279 prvSocketConnect Retrying connection with backoff and jitter.
sockets_wrapper.c +161 Sockets_Connect Established TCP connection with . socket=0, ip=-747515379
core_mqtt_serializer +969 deserializeConnack CONNACK session present bit not set.
core_mqtt_serializer +911 logConnackResponse Connection accepted.
OtaOverMqtt.c +1383 prvMQTTConnect Session present: 0

Seems like you are using mbedTLS. Would you please enable mbedTLS debug logs and share complete logs?