Blank thumbnails, no pdf shown on pdf page

QuestionsCategory: PDF Light ViewerBlank thumbnails, no pdf shown on pdf page
davor asked 5 years ago
displaying thumbs like:
[pdf-light-viewer-archive title=”” categories=”cat1,cat2,cat3″ posts_per_page=””]
some thumbnails are blank
when clicking on thumbnail, page shows title correctly but no pdf is shown, error console shows no error
is there a step by step working tutorial for creating categories with thumbnails like in this example:
https://pdf-light-viewer.wp.teamlead.pw/pdf-archive-for-particular-category/
https://pdf-light-viewer.wp.teamlead.pw/archive-shortcode-demo-masonry-full-thumbnails/(here are blank thumbnails also at example page, how to replace with custom image)