The configuration looks correct to me, it should be fine that way.
– Are the custom fields text based fields, or something comlex (like objects, some kind of selector, etc..)? I only recommend using text or textarea input fields (if using ACF) to store the keywords. Other fields might have different storage, and might not be visible for related posts pro in the database.
– Another thing might be the keyword occurence. By default, the plugin only considers words that occur 2 or more times within custom fields as well. On the Relevance Options -> Keyword options panel, try changing the Minimum Occurences option to 0 and also, try increasing the Keywords maximum count option to 10: https://i.imgur.com/tfFdKxt.png
When testing these options, I recommend turning off your site cache, and the related posts cache as well on the Advanced Options panel: https://i.imgur.com/FzPr9CD.png
I hope this helps!Best,
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