This is a frequent question posted by frustrated business owners.
"Trying to build up our company's GMB reviews. I received an awesome review yesterday from a recent client -- it was very kind and thoughtful -- exactly the sort of thing I want on my GMB page. In less than 24 hours, the review was taken down. I haven't had that happen to any other reviews.
The reviewer did the review at his home (not at our office), did not put any URLs or email addresses in the review, etc. I don't see that it violates any rules."
Ask For An Edit
GMB has an automatic review filter that kicks in sometimes and if everything else is kosher about the review, it might be a simple case of tripping the filters by accident.
Try asking the person who left the review to edit the review. They don't need to edit much, just a few tweaks. Sometimes that will cause the review to stick once they re-publish the review.