Introduction
When both a video and featured image are added to a post, the featured image will be prioritized only by widgets that allow selecting between the two. For some themes such as Motion Picture and Gigawatt, videos are prioritized in the blog feeds and slider.
This is working as designed.
The Solution
The slider prioritizes videos even if you have a thumbnail added, you can force the slider to ignore videos by editing a theme file.
Gigawatt
For the slider:
Open /ocmx/widgets/slider-widget.php and change line 32:
$image = get_obox_image(940, '530', 'thumbnail', '', '');
to
$image = get_obox_image(940, '530', 'thumbnail', "", "", false, true);
For the blog feed:
Open /functions/fetch-list.php and change line 2:
$image = get_obox_image(550, '250', '', 'div', 'post-image');
to
$image = get_obox_image(550, '250', 'thumbnail', "", "", false, true);
Motion Picture
For the slider:
Open /ocmx/widgets/slider-widget.php and change line 35:
$image = get_obox_image(580, 326, 'thumbnail', "", "");
to
$image = get_obox_image(580, 326, 'thumbnail', "", "", false, true);
For the blog feed:
Open /functions/fetch-list.php and change line 2:
$image = get_obox_image(580, '200', '', 'div', 'post-image');
to
$image = get_obox_image(580, '200', 'thumbnail', "", "", false, true);