in production associated fields disappeared

[rodinux]

After updating my rails app, and all the gems, in production I can't see no more the fields for 'actualize if exist'.
I find a solution with these lines on rails_admin.rb on the models.

import do
       mapping_key :id
       exclude_fields [:created_at, :updated_at]
     end

But it is like if I was blind. Anyway, on the development environment, I can see the fields as before for 'actualize if exist'...
some of my specs:

ruby 2.6.3
activerecord (6.0.0)
rails (6.0.0)
rails_admin (2.0.0)
haml (>= 4.0, < 6)
rails_admin_import (2.2.0)
      charlock_holmes (~> 0.6)
      rails (>= 3.2)
      rails_admin (>= 0.6.6)
      simple_xlsx_reader (~> 1.0)