What we have to know is the difference between fail & drops.
SDCCH Fail ==> it simply means that channel SDCCH hasn’t seized the TImeslot in TRX. It’s sometimes due to SDCCH Congestion, TRE Faulty which carries SDCCH TS or even bad SDCCH TS in TRE.
SDCCH Drop ==> it means that SDCCH channel has seized SDCCH TS in current TRX, but due to bad radio condition (Qual, Interference), then this channel drops. It’s also due to BAD SDCCH TS.
I suggest you to re-allocate SDCCH TImesot to another TS. Remember to pur the SDCCH TS not in TS0.
Paul C S