am I doing something wrong re: Rails with_lock?

For Rails versions from 4.2 through 5.1.7 the code below worked fine.

In Rails 5.2, in my Rspec tests, unless I add an extra reload (shown below as a comment), it fails with the exception:

ActionView::Template::Error:
  Locking a record with unpersisted changes is not supported. 
  Use `save` to persist the changes, or `reload` to discard them explicitly.

Since the call immediately before the with_lock is a save (as per the exception message) why would this still trigger an exception unless an extra reload is added right after the save?

  # merge into the serialized hash field 'settings' a new hash
  def update_settings(hash)
    return if hash.class != Hash
    return if !hash || (hash.count == 0)

    self.save # flush any pending changes
    # self.reload # <<<<< WHY MUST THIS BE added for rails 5.2?
    self.with_lock do
      mysettings = self.reload.settings
      # mysettings = self.settings
      hash.each do |k, v|
        mysettings[k] = v
      end
      self.update_attribute :settings, mysettings
    end
  end