Rails Redis Cache stores empty information out of method

My user.rb (model) has the following instance method:

  def points_last_seven_days    last_seven_days_hash_raw = self.reports.group_by_day(series: true) { |r| r.created_at }    out = {}    last_seven_days_hash_raw.each do |day, reports|      out[day.to_s] = reports.last.bullets    end    out  end

When i run User.first.points_last_seven_days everything goes ok, as expected i get an hash with data.

Now comes the tricky part.I have a cache module loading User into redis.

For that i use, among other things:

    def make_cacheable_strings      output_array = []      get_users_for_status.each do |user|        output_array << user.to_json(methods: USER_CACHED_METHODS)      end      output_array    end

My USER_CACHED_METHODS are as follows:

  USER_CACHED_METHODS = [    ...,    :points_last_seven_days  ]

The point is: User.last.method_name = correct data
CachedUser["method_name"] ( json redis ) = {} // empty hash...

What is happening?
Thank you