We need to have the "Assignee" field in your JIRA project settings to be shown. Here is how to check and show the "Assignee" field. 

1. Open Project from Jira and click "Settings"

2.Click "Fields" to open field setting.

3. Click Edit icon for Default Field Configuration.

4. Please check that the Assignee field is shown. (If it is hidden, the Actions should have "Show" link. If it is shown, the Actions should have "Hide" link.)

Note -- if "Assignee" field is now shown, Worksnaps always retrieve 0 minutes from JIRA.