Google is systematically check business profiles and removing reviews that violate the TOS. It appears that the they are getting more aggressive this week as lots of people are having the same complaint.
Any review 1 to 5 stars can be in violation of Google’s TOS. Google can see how the reviews were posted and from where and use that as a deciding factor. They could see issues with the profiles leaving reviews and remove the profile. The reviews could be left using software that violates the TOS. The profiles could be leaving reviews for more than one location and then get removed. There is no way any of us to know and Google won’t share why the reviews were removed.