a couple things. PERMISSIONS (do you have permission to view ALL of them). GRID VIEW Layout. If you have the Tags page in GRID VIEW and you have the option of "Require Image" and some of those don't have images, they won't be displayed.
This thread is referring to the OLD Legacy Tags system that used to be in Showcase. He was having an issue with the Showcase Tag Cloud. That entire system has been removed and replaced with the Core XF Tags Handler.
With that said, can you reproduce the issue YOU are having here? eg, create the same item here (you have full permissions to do so), add tags to it and then look at the Core XF Tag Cloud on the search page. If its working here and not on your site, then I will need access to your site to troubleshoot (just like I did with the above individual). I'll also need DB access (phpMyAdmin) so that I can see what data is in the "Tags" related tables (both core XF and Showcase). Just shoot me login credentials via inbox with any special instructions. More than happen to check things out