This is common with Google. The reviewer can see the review but Google's algorithm blocked it from publishing live.
Unfortunately we aren't able to control what reviews Google publicly publishes. Google will hide reviews for a number of reasons that we are unable to see. It could be that the reviewer has had their profile flagged, or in some cases it could take up to several days before the review is publicly visible. Even though everything checks out and you may think a review should be showing up, Google will still filter reviews based on their ever-changing algorithm.
Not all Google reviews will show up publicly on your GBP listing. The best way to combat this is to get more Google reviews.
The review link that customers leave the review through does not effect if the review is published or not. The review link directs your customers to review platforms such as Google. The end result would be the same if the customer searched you on Google to leave a review, or if they left a Google review through the review link.
If you have any further questions please reach out to [email protected].