Inherited Tasks in Templates / Custom Fields in subtasks missing when converting to Template

I want to keep a Custom Field (with a selection on it) in a Sub Task in a Template. The Custom Field relates to a Project that I’ve added to the Sub Task in the Template (which falls within a separate Project) but I can’t see the fields. I’ve tried creating this as a Task and then converting to a Template but that’s not working either. Any tips?

Can you share a couple of screenshots? I am not sure what you mean. Keep in mind a subtask can have its own fields if multi-homed in a project, but a subtask also inherits the parent task projects fields…