Your plugin is great and does good job. However, I found few issues:
1. When I save the options in settings page, I am getting warning saying:
Warning: addslashes() expects parameter 1 to be string, array given in \myserver\mysite\wp-content\plugins\yet-another-related-posts-plugin\options.php on line 77
2. I have huge amount of tags like 5000+, as my site has huge number of posts. Whenever I try to access settings page, it takes huge time to load and uses huge resources. Because of that, my hosting suspended my account couple of times. I think it is because of loading all tags and categories on settings page. Instead of that you may provide a text box and the user can enter the list of tag/category ids in the text box provided.
3. As I said my site have 5000+ posts & tags, if the related posts cache is not completed and the plugin tries to build the cache on the fly when there is no cache is built. Because of that, again it takes huge resources and the doesn’t load even in 2 mins.
4. when I try to build the cache, I am getting error saying timeout occured.
BTW, I am using latest version of WordPress and YARP plugin.