Reasons why the adjacent cell of a site fails its handoff

Hi Experts.

Any idea why the adjacent cell of a site fails its handoff?
Is it noise, interference?

Does it fail 100%?
Maybe not enough overlaping, maybe HO parameters are too tight.
Do you get radiolinkfailure instead of handover execution?

Not 100% but does not pass the 99% only 88%.

Is it lab cell or live network cell?

Maybe you have conflict PCI.
2 neighbors with same pci, both overlaping with source cell.

Live network.

PCI conflict is not possible, because same site but different cels.