If image uploaded to Gallery will have smaller width than 150 px - there is no fallback, so there will be no thumbnail and thus no image preview in Admin.
This will also generate:
Notice: Undefined index: xs in C:\xampp\htdocs\batflat\inc\modules\galleries\Admin.php on line 133
Basic workaround (it will treat image itself as thumbnail):
If image uploaded to Gallery will have smaller width than 150 px - there is no fallback, so there will be no thumbnail and thus no image preview in Admin.
This will also generate:
Notice: Undefined index: xs in C:\xampp\htdocs\batflat\inc\modules\galleries\Admin.php on line 133
Basic workaround (it will treat image itself as thumbnail):