Without cracking open the alerts this may be hard to tell. I would have to see the xml breakout of that alert to even be able to tell you if there is an empty or incomplete data set, as I do not think any report I have would highlight a 'blank'. More than likely the detail would not be there, so the condition might seem incomplete upon review.
If you did import some alerts, you would need any Custom Properties already created so they could be used and mapped within the alert. You could set the value of said CP's after, but the CP would at least need to be created. If this is the case, create the CP. Delete and re-import the alert.
If these alerts were not imported then I would expect one of two things, the xml file was manually edited; or there is a bigger issue going on with your system.
You might be able to see errors in the alert logs and pick them out by alert id that shows in the logs (possible long shot).
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