I've imported some Sub-Tasks to Jira via CSV file. The idea was to connect Sub-Tasks to existed Stories. Some Sub-Tasks were connected to Story as expected but only one Sub-Task per Story. Rest Sub-tasks were imported to Jira as well but with no parent. Unfortunately I can't change 'blank' Parent for such Sub-tasks to existed Parent issue. I'm getting error 500 every time I do that.
Any ideas how to solve that?