Thank you for using WRI.
We have several ideas to try:
You may need to save YARPP settings in Settings -> Related Posts (YARPP) menu, to refresh the settings. So please push “Save Changes” button on “Related Posts (YARPP)” options page even if you don’t change any YARPP option. This is often help to resolve such problems.
Similarity thresholds can also cause problems if they are not adjusted properly. Please go to Settings -> WP related Items menu and chose “Products Page” tab (if the problem is occurs on products page). Set low threshold value for every post in “Match threshold” column.
You can try to enter the value 1 as thresholds, and if you get related items, you can increase the value (if the value is too low, less relevant items will be displayed). So you can find the optimal threshold value.
One more check: Please go to the edit page one of your product, and try to set some related posts and products manually. You can do this on Edit Product page, find “WRI Manual Relationships” metabox, and drop some items to the right side, then Update (save) your product. This way you should definitely get some related items displayed on this product page.
I hope we can help you, please let me know if you could solve the problem, or is it still there.