If I had to guess, make sure there are no require/include/instance_eval of the :pais3_prod_backup model file in your backup config.rb (or some include of all models from models/ folder).
I fell for it when upgrading from version 3.x to 4.x, and it took me several hours to figure out why all my models are running twice. I solved it by removing the following code from my config.rb:
# Load all models from the models directory (after the above global configuration blocks)
Dir[File.join(File.dirname(Config.config_file), "models", "*.rb")].each do |model|
instance_eval(File.read(model))
end