High sdcch drop due to other reasons could be lead by :
1. Transmission Flicker
2. Power issue
3. Hardware issue ( DRU, TX or RX ) Trial Lock and Unlock absolutely working and hourly monitoring.
4. Sleeping DRU suspected ( Increased SDCCH Drop > 15 %, Tch Assignment succes rate < 90 % and Ho Incoming succes rate < 95 %. Good Luck Knowledge for sharing but keep learning don't just asking