Surface Validation Errors as Issues with Specific Lines

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Many validation errors are currently surfaced as a result of a failed if not all(..) check. This results in generic error messages with no hint to the user as to which variant(s) are problematic.

The user experience would stand to improve if such errors were surfaced on a line-by-line basis, so that users who upload data and experience such validation errors can fix them expediently and have a better sense of what the issue is.