We're not able to reproduce the issue in PHP 7.1.2 with bender + branch hotfixes, could you tell us something more to be able to?
the proposed change : $aItem['photos'][] = Params::getFiles('photos'); doesn't make sense, because you are putting the images in the wrong variable (inside an array), so probably no error, but images will not be uploaded either.
Not really sure what fancybox/jquery has to do with this, if any, it should be fineuploader. We know it's outdated, but new versions are not as compatible as we would like to, and require changes in the HTML/template among other things