You need to add parentheses around your code:
Before:
$reference->frotel_vitrine = empty($item->special) ? null : $item->special == 2 || $item->special == 3 ? 'active' : 'deactivate';
After :
$reference->frotel_vitrine = empty($item->special) ? null : (($item->special == 2 || $item->special == 3 )? 'active' : 'deactivate');
That should solve the issue.