Inter-eNodeB X2 based HO preparation failure rate increase to 90% for one site

Hello Guys,
I have a inter eNB X2 based HO preparation failure rate increase to 90% for one site.
Do you know the possible causes of this issue?
Someone has already encountered this problem?
Vendor is Nokia.

Preparation can be due to TNL in neighbor.
Check ncell which nbr has increased, preparation issues.

Maybe X2 faulty, wrong configure external cells PCI, TAC, eNB ID, or target eNB user congested…

Yes, it can be due to this too.

Preparation failure mainly due to definition issues.
Without getting much into detail, you can just go for deletion and recreation.

Maybe PCI confusion?

Preparation won’t fail in PCI confusion.

Yes, PCI confusion will cause HO execution fail, not HO preparation fail.

X2 link admission reject tnl and external configuration, major reasons.
And if prep but no exec att at all, then nbr missing.

Almost due to external cell/site configuration problems.

TNL is sudden prep att.
With less exec att happening.

Are you enabling any load balance feature (IFLB, AMLE)?

How does load balancing can impact X2 HO?

Legacy IFLB could cause this, if it goes from high BW to low BW, as there is no target load for this feature, just target RSRP & RSRQ.

This might be due to target ip is not reachable… Check if S1 is ok between these nbrs. Just delete the nbrs and let the nbrs recreate by Anr. Also you can try for destination based routing.

Locate the problematic target cell with high “HO Prep fails due to others” and zero HO prep attempts. In case of no ANR, allocate the correct S1-C/X2-IP, refresh the link, system will itself pick the IP and X2 alarms will disappear.
Other options could be, TAC & PCI mismatch or definitions update issue.

This is bcoz Target cell is not responding to source cell… Mainly happens when target cell do not have resources.