Normally review records don’t get updated after they have been created. But recently the WK devs have been backfilling the review data to align with API changes on the backend: they’ve added and removed attributes related to this big backend change:
The result is that the updated timestamp gets bumped, even though the essentials of the review result haven’t changed.
The records you are mentioning are probably from before this change, and have been touched by that process. And the more recent review records will most likely be untouched. Your code should allow for the possibility that these kinds of changes will happen occasionally.