It is possible to clone Custom Fields with Deep Clone for Jira. If some Custom Fields weren’t cloned, you can try the following solution.
The Custom field must be configured in both projects.
The name of the Custom field must match in both projects if you clone between company-managed (classic) and team-managed (next-gen) projects.
Some Custom Fields are automatically set by Jira and cannot be edited by Deep Clone:
"Date of First Response"
"Username of last updater or commenter"
"Domain of Assignee"
"Domain of Reporter"
"Number of attachments"
"Number of comments"
"Last public comment date"
"Last commented by a User Flag"
"Participants of an issue"
"Days since last comment"
Some custom fields can not be cloned at all:
"Rank" - However, you can use the "Rank cloned issues" function after a Bulk Clone instead.
"Development" - Is set by the respective development tools integration of the Jira project.
Some Jira Service Management fields can only be cloned with restrictions:
JSM "Request Type” - Only supported with “Immediately clone issue” and if the issue type stays the same (JSM limitation).
JSM "SLAs" - Automatically set by JSM
JSM "Approvals" - Can only be set by JSM. Get in touch with us, if you need to clone this field.
JSM "Satisfaction" and "Satisfaction date" - Can only be set by JSM
JSM "Request language" - Can only be set by JSM
Disabled options in select lists cannot be cloned at the moment.