During drivetest, is the co-site neighbour being reported ?
What about indicator : do you see ho request between the two cells ?
If the neighbour is reported, then the BSC shall be able to trigger a handover.
If the HO command is sent to the MS, it means there is a ho request + ho allocated –> you should then see a HO failure (1 attempt w/o success = one ho failure in drivetest)
Altogether, you need to make lot more investigations, in order to isolate the root cause.