I'd like to correct my answer above with a more straight-forward approach. I used the Interchange events to trigger a callback function that inits the Masonry grid. This works well and has given me no problems.
Here is the event as listed in the docs:
$(document).on('replace', 'img', function (e, new_path, original_path) {console.log(e.currentTarget, new_path, original_path);});
So just create a function to init the masonry grid, and call it from within the code above.