it’s probably one or few faulty MS which are going crazy. the only way to investigate this is to trace the A interface and correlate the IMSI or IMEI with the phone brand/model.
– too short value for T3212
– bad LAC design : check that the neighbours do have the same LAC indeed
– MS attaching to your network because their own network is down (collocated BTS from another operator is down, for example)