Redmine

Eventually I was able to make the following code work with Redmine 4

namespace :redmine do
  namespace :myplugin do
    desc 'Updates custom field for idle tickets.'
    task :update_idle => :environment do
      Issue.open.each do |issue|
        begin
          days = DateTime.now.to_time - DateTime.parse(issue.updated_on.to_s).to_time
          days = days/86400
          if days > 0
            issue.custom_values.each do |x|
              if x.custom_field_id == 19
                x.value = days.ceil
                x.save
              end
             end
            issue.save
            true
          end
        end
      end
    end
  end
end

Could you try again after changing all save method to save! method?

save! thorows an exception when it fails. Probably it is useful to troubleshoot this issue.