Callback raising initialize_method is not a function

I have a page with a single map and sometimes I get a 'initialize_method is not a function' error and the map doesn't load. Using cornford/googlmapper v 2.32. I have async set to true but still encountering this error.

Controller:

Mapper::map($lat, $lng, ['zoom' => 14, 'marker' => true, 'center' => true,
                  'draggable' => true, 'streetViewControl' => false,
                  'mapTypeControl' => false, 'fullscreenControl' => false, 'async' => true,
                  'eventAfterLoad' => 'mapLoaded()']);

Blade:

<div id="listing-map">
    {!! Mapper::render () !!}
  </div>

Error:

bradcornford / Googlmapper

Callback raising initialize_method is not a function #285