I'd say the filter works correctly, InspectionDue le addDays(utcNow(),60,'yyyy-MM-dd') will return all items where InspectionDue <= 2020-12-29, and all the dates you shared are less than December 2020.
You should put there also bottom limit for today's date to get only items with InspectionDue between today and today+60.
InspectionDue le 'addDays(utcNow(),60,'yyyy-MM-dd')' and InspectionDue ge 'utcNow('yyyy-MM-dd')'
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