Is it OK for you to share the address to your A-Z page?
I’m not sure why the posts would all filter into the # category unless the alphabet has become confused. Are the alphabet letters that the plugin is using matching at least some of your posts’ first letter of their title? Could you give me an example of one or several posts’ titles that have been filtered into the wrong category (in lieu of a link to your site)?
Also, could you try to find out what PHP version your site is running and whether the PHP module called mbstring is enabled? – I have put workarounds in place for sites that don’t have mbstring, but I haven’t got automated tests that prove their correct operation yet so I might not have got it working properly for such setups.
I have added few dummy posts
The page looks correct to me. The # category is correctly elided, because there are no posts within, and the posts shown are all filtered into the correct categories. Could you elaborate a bit further on how the listing is broken because I can’t see any incorrect behaviour in your linked page?
I am not using your plugin now. But help me if you can with your plugin. Thanks. Let me use your plugin on another page.