There are dozens of reports from business owners complaining their reviews listing on their Google Place pages are missing, or many are. There are many threads with complaints, but I’ll link you to one at Google Places Help.

In that thread, Googler Stephan S. said:

The thing is, many are still missing reviews. Typically, if a review goes missing they’ll come back, eventually. But maybe when Google divided the reviews it caused some additional issues?

Forum discussion at Google Places Help.