did this happen at once or have there been changes in your Jira?
I am thinking of any configuration chance you probably made (or a second admin of your Jira)?
Is it new "new issue view" of a classic project you are viewing - if so, can you switch back to the old issue view?
Here is a thread where this problem also showed up - along with some information and debug.
In case this does not help please provide further details.
Thanks to @Daniel Ebers
Following your suggestion about change to the old issue view, I saw the actual error message, which was about the default assignee issue.
Recently, I have removed the project lead person from Jira and it was set to default assignee, system couldn't create a new subtask
I just changed the project lead and it fixed.
When to use CSV importer When managing your processes in Jira, there are many occasions where you need to create a lot of tasks. Creating them one by one will cost you a lot of time and effort and i...
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