In the new UI for Validation to view failed test classes error messages you must click into each failed class to view the details.

The previous UI showed "part" of the error message within the table. This was extremely useful in identifying all of the "unique" errors that are occurring.

IE: If 58 test classes fail from "4" unique issues -- then in order to determine that you may need to click into all 58 test classes or fix one at a time --> refresh --> validate.

This is just a time save feature.