We’re not working with the same equipment as yours, but there are some concepts that are shared by all vendors.
What you could do is, on the TRX / Air interface:
1/ change the position of the SDCCH timeslot (to another TRX)
2/ add another sdcch timeslot (on a different TRX)
On the Abis / BSC interface, try locating your sector on another BSC board (called TSU / TCU in alcatel), so that all signalling messages are handled by another BSC board than the current one.
You are not measuring any call drop (tch drop) ? Since TCH and SDCCH are sharing the same abis link, it means your abis is probably fine. You can focus on the signalling boards only.
Now, i don’t know the specifics of your vendor, but it might be software related also? In this case, deleting and recreating the sector in the OMC might solve the problem. Or might not… 🙂