A Google Maps Help thread has several business owners complaining that their reviews listed on their Google Maps listing have mysteriously disappeared. Some reported all of their reviews are missing, whereas others reported only a portion of their reviews are missing.

Googler, Brianna said:

Google Maps & Local guru, Mike Blumenthal, gave a bit more insight from outside of the official Google cloud. Mike expalined:

Are you missing your Google Maps reviews recently?

Forum discussion at Google Maps Help.

Update: This should have been resolved later on this day.