HOSR (Handover Success Rate) issue from G900 to DCS1800 cells even in co site

Hi Dears.

In our 2G network, Huawei Vendor, we have DCS 1800 and G900 cells (no concentric cell).

Recently we faced HOSR (Handover Success Rate) issue from G900 to DCS1800 cells even in co site.

HO attempt increased and most request failed.

Do you have any Idea, what is issue?

Hosr reason is better cell.