502-Whoops, GitLab is taking too much time to respond

We are using the GitLab Community Edition 8.14.3 omnibus installation.

After given the merge request, I can not able to view the merge request details when I click the merge request on the website. I do not know why this happening? But this request contains nearly 70 changes. But over all size is less than 1MB.

I got the error in the pipeline which is shown in the merge request.

When I click the above link. I get the 502-Whoops, GitLab is taking too much time to respond error page.

I don`t know the head or tail in this case. Because we are recently moved to GitLab.