Attributes are visible in the admin/Attribute Category preview, but do not show when creating a project from a template which uses this attribute category.
There are two possible reasons:
The attribute is not in the Creation view of the attribute category.
The attribute is hidden through a rule.
You can see the difference via the Attribute Category preview in admin/Attribute Categories:
Check which view exists. If a Creation view exists, it will be used by the project creation. Change the view to Creation and verify that the missing attribute is present. If not, you may want to add it.
If the attribute is present, check its rule (in the Details).