Multiple files not attaching to field

[nickjacobs]

I have added a SortableUploadField (on a silverstripe-elemental block) and it works fine when uploading images one by one - but when I try to drop multiple images in (or even select multiple using the 'upload new') the images load into the correct assets folder in the background, but don't attach to the dataobject, and don't display as loaded in the field...

Pretty standard setup:

private static $many_many = [
        'Images' => Image::class
    ];

$fields->addFieldToTab('Root.Main', SortableUploadField::create(
                'Images', $this->fieldLabel('Images'))
                ->setFolderName('ImageBlocks/'.$url)               
        );

[bhofstaetter]

Should be related to https://github.com/silverstripe/silverstripe-elemental/issues/815