Merge request was not shown in the Git integration panel

[yuliangwei@cloudwalk.com]

we have gitlab integrated via git integration plugin, in most of the cases, it works very well, however sometimes the merge request was not shown in the git integration panel on the jira issue page, you can see the screenshot for reference.

and sometimes it works

see below screenshot, please ignore Chinese, sorry aout that.

I'd like to know 

1. why the merge request was shown as link but not in the git integration panel

2. sometimes it works, why? any configuration I should check?

Thanks.