Do you know what happens when a foreign MS attempts to connect to your network ? Perhaps the location update is rejected, but without the proper msg on the air interface.
So the MS still waits for an answer until there’s a drop..
you could check the average duration of the sdcch, if it’s higher than before ?
otherwise, try putting more “tch preference” priority on the TRX that carries the SDCCH timeslot, so that more calls are established on this TRX.
If call drop increases, then it’s a problem related to the radio of this TRX.
If the call drop is stable and traffic is succesfully handled by the “sdcch trx” , then the problem is indeed on the signalling part.