RF9151 DK connects to nRF Cloud via CoAP, but MQTT / public Internet not accessible (Conexa SIM)

Question

Hi Nordic team, 
 I'm currently testing the nRF9151 DK with a Conexa IoT SIM card in the United States (Philadelphia area). The board is flashed with the Asset Tracker v1.2.1 sample firmware, using nRF Connect SDK v3.1.99. 
 The device successfully connects to LTE-M and provisions to nRF Cloud. 
 Status on the nRF Cloud dashboard: Provisioned CoAP connection authorized (result code: 2.01) 
 Log example: [00:00:12.359,252] nrf_cloud_coap_transport: Authorization result_code: 2.01 [00:00:13.398,010] cloud: nRF Cloud CoAP connection successful [00:00:13.398,254] cloud: Connected to Cloud 
 So the Asset Tracker (CoAP) mode works fine for provisioning and cloud data updates. 
 However, when I try to test general Internet connectivity using the AT interface (via Serial LTE Modem firmware or the Asset Tracker shell), the following commands fail: 
 AT+CGDCONT=1,"IP","conexa-iot.us" OK AT+CEREG? +CEREG: 0,5,"56D8","0DA90315",7 OK AT+CGPADDR +CGPADDR: 0,"100.117.182.54" OK AT+XGETADDRINFO="google.com" ERROR AT%XDNSCFG? ERROR 
 This shows that LTE-M attaches successfully and an IP address is assigned, but DNS resolution and public Internet access both fail. 
 My current understanding:

The Asset Tracker firmware uses CoAP over a private nRF Cloud channel, so it connects fine even when the SIM cannot reach the public Internet.

The Serial LTE Modem (SLM) firmware can attach to LTE and get an IP address, but cannot resolve DNS or connect to external servers.

Therefore, it seems that the Conexa IoT SIM APN (conexa-iot.us) only supports private core traffic and does not provide public Internet breakout.

Questions:

Is this expected behavior when using private IoT SIMs like Conexa with nRF Cloud?

To test public MQTT or HTTP data transfer, should I use a public IoT SIM (such as Hologram, 1NCE, Verizon, or AT&T)?

Does Nordic recommend any SIM or APN configuration that supports both nRF Cloud and general Internet access?

Test setup:

Hardware: nRF9151 DK

Firmware: Asset Tracker v1.2.1 and Serial LTE Modem

SDK: nRF Connect SDK v3.1.99

Modem FW: mfw_nrf9160_1.3.x

SIM: Conexa IoT (APN: conexa-iot.us)

Location: Philadelphia, USA

Thank you for your time and support. Best regards, Linhai Deng