omsocombb not receiving calls

Hi, I would first like to thank all those who participated in this nice project. I recently started working with osmocombb and was able to have it working fine on a motorola c118. However, I noticed that some sim cards can connect normally to the BTS, can make calls and send SMS but can’t receive anything. They simply don't get paged. While for some other sim cards everything seems to be working fine. Does anyone know what might be causing this issue ? thanks, Robert