Thanks for the proper details, I was able to find the problem.
In your configuration posts and pages were selected as related content sources, and at the same time category and portfolio category matching was enabled. Since posts and pages does not have the portfolio category (so it does not match the criteria), nothing was displayed. I've changed the configuraion to look in posts and portfolios, and match tags only, to prevent missing posts. Now it should display items correctly.Best,
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