One business owner said:
we have in the last week lost all of our tripadvisor reviews from our google place page...
Mike received a statement from Google saying it is a bug and the reviews will return. Google told him:
We're aware of a technical issue in which TripAdvisor reviews are sometimes not appearing in results for Google Places, and our team is working to resolve the matter.
So if you lost reviews, this may be why.
Forum discussion at Google Places Help.