This can usually be a problem when the SIM card is not read or is in it. In case you use a different card and it works the problem is in the cards, otherwise it can be more difficult to solve it, in case the problem is in socket. One of my friend had a problem like this, as i understood from he tried to do some modification with the sim cards, to change the codes there. As I remember he used https://www.sccatl.org/ and 2 more programs, but it was not possible to do anything, the socket came with some problems.
I’m confused about why you are responding to this thread. The issue has been resolved. The original motherboard and cellular modem were defective and were replaced. I now have a fully working system using my original T-Mobile SIM card. All is well.
I find if I install the drivers for the em-05a and they show correctly in device manager but will not work or show any cellular in the taskbar. As soon as I uninstall the drivers and it defaults to just 4 em-06a in device manager it works fine I have 20 devices all working this way. If you are having issues try uninstalling the drivers from seeed and just use basic found hardware. SNO