Simple date query not working after 2016

I am using a custom post type with custom fields to display tour dates on a page. Some of the posts have both a "from" and "to" date (because they last for more than one day) and some only have "from" (because they're only one day), and I want all future or current tour dates to be displayed.

It's all working perfectly, except for some reason the posts that only have a "from" date stop showing if that date is in 2016 or later. I'm very confused!

Here are the args:

$today = date('Ymd');
$tour_args = array(
	'post_type' => 'tour_date',
	'posts_per_page' => -1,
	'orderby' => 'meta_value',
	'meta_key' => 'tour-date-from',
	'order' => 'ASC',
	'meta_query' => array(
	  'relation' => 'OR',
	  array(
	    'key' => 'tour-date-from',
	    'value' => $today,
	    'compare' => '<=',
	  ),
	  array(
	    'key' => 'tour-date-to',
	    'value' => $today,
	    'compare' => '>=',
	  ),
	),
);