Hey Ian, thanks for reaching out! That's a good one and happy to check it out if you have the link to the table...What comes to mind and the recurrent situation we see is that if you select a validation provider like Debounce or any of those options, those validation columns are automatically hidden but you can reveal them at any time like any other enrichment.
What happens is that if the first email provider finds an email, the validation tool may be saying it's not a valid email so it then let's the next provider run to try to find a new one but if that other provider has the same email then it won't try to validate it again unless it's different. If no other option is found, then the final results will be empty.Let me know if that sounds like it may be the case here and if you have additional questions!
The advantage of using the email waterfall with these providers is that it doesn't cost any credits if they don't find one, but unfortunately, the coverage could vary quite a bit. You can always add a new waterfall with other providers and give it a condition to only run for the empty/missing rows