String in merge request title is replaced by commit number

My server is running with GitLab CE 9.5.9. One of the users reported a issue related to merge request title.

In the attached image(1), you can see merge request title properly updated. [WIP] Merge ntas-17-0-sp1_FC015135-FC014993

When i click open the merge request, it is showing different title. One string is auto replaced by a commit nummber as shown in the image(2). [WIP] Merge ntas-17-0-sp1_277d262a-FC014993

Can anyone help on this to identify what is the reason for this issue?