In the image above every iteration has its validation rule occurred, I wonder if there were more validation rules, does the execution log show all of them in every iteration or show only one indicating that the record in the iteration has one or more validation rules?
There would only be one CODE_UNIT_STARTED and CODE_UNIT_FINISHED per record per evaluation (e.g. if there was a recursive trigger, you would see another validation in the recursion).
If you change your Debug Level to include Validation: INFO, you will also see the following items: VALIDATION_RULE, VALIDATION_FAIL, VALIDATION_PASS, VALIDATION_ERROR, and VALIDATION_FORMULA. In that case, you would potentially see multiple VALIDATION_RULE entries and which ones passed/failed if you had multiple rules.