what do you mean by “failing” : are you seeing this during drive-tests, or on QoS statistics ?
During drive-tests : there is handover failures, or just there is no ho while you’re expecting one to occur ?
With QoS : do you see HO Request, HO Command, HO Success ? If there is a failure, what is the cause of the failure ? Congestion, Radio problem, with or without Reversion to Old Channel ?
What about the target cell : does it accept HO from other cells ? Without failures ?