Symptom:
The same issue was observed and its reported as part of CSCul92988 when RAC is 0.
[local]SGSN-MME-01# show subscribers summ gprs-service 2g-sgsn nsei 143
No subscribers match the specified criteria
[local]SGSN-MME-01# show gprs-service name 2g-sgsn | grep -i 143
nsei 143 name BSC-03-Krasnoyarsk-Kansk
nsei 143 : Pooled
nsei 143 lac 24111 rac 0 
nsei 143 lac 24112 rac 0 
nsei 143 lac 24110 rac 0 
nsei 143    DSCP Template     : signalling-dscp-template

Conditions:
As per the webex we had 
-> There was one nsei ( one BSC ) working perfectly fine with 3 LAC/RAC values. Then those LAC/RAC values were changed to some other values on both the BSC & SGSN side. 
    After that activity the traffic was not seen particular on those LAC's and the attach requests were not accepted on that. 
-> We double confirmed that LAC being used are same on both sgsn & bsc side, and now the bsc is migrated to the other operator's sgsn where it is working fine