Well, I work on this wordpress site within a company, so I rather do not public the url of this development site, on real site it's now done by data-slb-group as I posted.
In functions.php there is a function that prints all posts in one category, each post has few thumbnails (by multiple thumbnails plugin). Via shortcode this function is invoked in a page. By get_posts() and get_the_post_thumbnail() all the thumbnails are displayed. Now I want to slideshow only these thumbnails, that are from one post. Problem is, that this (otherwise awesome) plugin does not recognize that and make slideshow for all thumbnails regardless which post they belong.
I hope I cleared this issue well.
Yes, "Group items by Post" is enabled, but just first option "Group items" has effect, others checked/unchecked has no effect in this case.
I admit, that with new version data-slb-group attribut can change and actual solition will break, but I have no better solution yet.
Thank for your time.