This scenario is applicable only if you are upgrading to Update 27 or a higher version.
Starting Update 27, the multiple values in the document review matrix columns are separated by a |. This replaces comma as the delimiter to avoid confusion when the column value includes a comma. When you upgrade, the system replaces any commas in the column values with a |. Hence, if you have an existing review matrix, you need to verify the column values in the review matrix and reselect the values.
The document reviews will not be generated for the affected rows if the above change is not made after the upgrade.
If you have any custom matrices or custom matrix rows, you need to verify the column values and manage the matrix accordingly after the upgrade.