Troubleshoot ActiveRecord callbacks; require/load this at the top of config/application.rb

callback_trace.rb

module CallbackTrace
  def self.included(kls)
    kls.send :alias_method_chain, :_compile_filter, :trace
  end

  def _compile_filter_with_trace(filter)
    generated_code = _compile_filter_without_trace(filter)
    return generated_code if filter.is_a?(Array) || @kind == :around || !(@klass.ancestors.include?(ActiveRecord::Base))
    "($stdout.print 'Callback: #{@kind} #{@klass.name}##{@raw_filter}'; $stdout.puts self.inspect; #{generated_code})"
  end
  ActiveSupport::Callbacks::Callback.send :include, self
end

You can also troubleshoot all ActiveSupport callbacks if you exclude the || !(@klass.ancestors.include?(ActiveRecord::Base)) bit at the end of line 8. When I wrote this up I was only interested in AR callbacks.