I read about your questions, MS need to decode BSIC of serving cell and Neighbor Cell due to camping on a new cell need this synchronization, otherwise, MS will know about to sync with the SCH;
The problem of MS can not get the Sync channel sometime, then, it will be several situtation you need to check :
1. If you use an Agilent Gsm/Gprs radio set to test with your MS, can it sync with its SCH ?
2. If you can sync with the above situtation, but MS is not able to sync with some SCH with some network, then, it need to check with several factor, is it a serving cell of BSIC that MS can not sync with or Neighbor cell of BSIC ?