Assign issue button and assign to me linkis not appearing on issue details in one project. In othet project it is working fine

[Nic Brough -Adaptavist-]

Check the permission scheme in the project.  For "assign" and "assign to me" to appear, you have to match the user permission "can assign issues".  I would say you do in most projects, but you do not in this one project.

See https://confluence.atlassian.com/display/JIRA/Managing+Project+Permissions