The SIM slot is directly wired to the MPCIe slot, so the modem has to talk directly to it. If anything goes wrong (on the modem, the PCIe slot, the SIM slot or the SIM itself) it doesn't work and the motherboard won't be able to tell you about it as it's not in the loop on that communication.
That means that the AT command sent to the modem will always be a bit of a black box since it cannot tell you where the problem is.
That means that the AT command sent to the modem will always be a bit of a black box since it cannot tell you where the problem is.
