I think I know why. On the product attributes panel, between the '|' separator characters, there are missing spaces (it should be added automatically when saving): https://i.imgur.com/sHvzol9.png
But, once I save the product, it's automatically corrected, and the attributes are indexed as well: https://i.imgur.com/7hZeDZe.png
I guess this might be because the products may have been imported in some way?
The explanation is that the '|' special character is not treated as a boundary, as it can be used in various fields.
Solution 1: To save all products so the attribute fields refresh properly
Solution 2 (recommended, faster): ..or to make a tiny change in the search plugin code to recognize '|' without spaces as word boundary as well. For this you will have to open the wp-content\plugins\ajax-search-pro\includes\classes\etc\indextable.class.php scroll to line 905 and change it from this:
$ww = str_replace(array('.', ',', '-', '_', "=", "%"), ' ', $ww);
$ww = str_replace(array('.', ',', '-', '_', "=", "%", "|"), ' ', $ww);
After that, make sure to create a new index, and the attributes should be correctly indexed as expected. I will make sure to include this change in the upcoming release as well.
If you need help with this, feel free to add temporary FTP details, and I will make the change for you.Best,
If you like my products, don't forget to rate them on codecanyon :)