Issue Summary

In Jira Software 7.1.0, a new feature was introduced which allows to flag Jira issues from Agile/Kanban boards, and which is explained in the documentation Flagging an issue.

If the Flagged custom field is set to Hidden in the Field Configuration scheme associated to a project, the issue flagging feature will stop working as expected for issues that belong to this project. For example:

• issues that have been flagged are not highlighted in the board and also no red flag is shown on the left of these issues
• for issues that have been already flagged, inconsistent flagging options can be seen depending on which dropdown menu is used

More information about these symptoms in the "steps to replicate" section below.

Environment

Issue replicated on Jira Software Sever/Data Center running on 8.13.x, 8.20.x.
The issue is not replicable on Jira 8.0.0, so it's possible that the bug was introduced in a version between Jira 8.0.x and Jira 8.13.x.

Steps to Replicate

1. Install Jira Software on version 8.13.0 or any higher version
2. Create a SCRUM project using sample data
3. Open a SCRUM board
4. Open the backlog view of the board
5. Right click on any issue listed in the backlog, and select Add Flag from the dropdown menu
6. Notice that now this issue is highlighted, and that it has a red flag next to it
   
7. Go to the Field Configuration Scheme associated to the SCRUM project
8. Search for the field Flagged and click on Hide to hide it. After it's hidden, a show link should show next to it:
   
9. Go back to the board backlog page

Expected behavior

The issue should still be highlighted, and a red flag should still be located next to it

For this issue, the same flagging options can be seen regardless of which dropdown menu is used:

• when clicking on the flagged issue, and then clicking on the "..." menu from the issue detail view, we can see the Remove flag button (expected behavior)
  
• when clicking on the flagged issue from the issue list of the board, the Remove flag button is also shown:
  

Actual behavior

The issue is not highlighted in the board and also no red flag is shown:

For this issue, different flagging options can be seen depending on which dropdown menu is used, while they should be the same:

• when clicking on the flagged issue from the issue list of the board, the Add flag button is showing instead of the Remove flag button (unexpected behavior)
  

Reference

This behavior is described in the Root Cause 2 of the KB article below:
https://confluence.atlassian.com/jirakb/the-issue-flagging-functionality-is-not-working-as-expected-on-boards-1130731678.html