This isn’t anywhere in the documentation, so I thought I would report it for anyone who runs into a similar issue. I was tearing my hair out over this for hours today.
If you have data in a data source that does not meet the data validity requirements (e.g. for an Enum column) it will still display in the app. HOWEVER, if you use the CSV export action to export a view, it will return a blank value for the invalid column in the CSV file instead of the value in the data source.