When duplicating Close Workbooks in Finance Close Automation, some of the Close Tasks (sn_fcms_close_task) do not have the Owner (assigned_to) field carried over to the duplicates. (FCA)

This is actually the expected behavior for the following reason:

The Product team introduced the new feature of Group Tasks.
If a task has an owner group set, any accountant in the Assignment Group can pick up the task and assign it to himself.

During duplication for a workbook for the tasks having an owner group, only the owner group is copied over and the owner is not copied to the new workbook.
The idea of group tasks is for anyone from the team to pick and work on it.

If you want the owner to copied during duplication, do not set the owner group in the tasks and only keep the owner.

Another case where the owner won't be copied is when the owner's user record is inactive.