is it my problem or Checkvist problem?
When you create due date tag, it is visible in rectangle withing task line. But when I duplicate task, suddenly it is copied as ^Jul 31, 2024 (date is just example). And I cannot do anything to display it back in rectangle, just delete and set due date again.
In the screenshot, it looks like also the tag isn‘t interpreted as a tag.
I‘ve copied a lot of dates and never had a problem. Maybe there is something in the line that distracts the parser? You can try to reduce the text to a single character and see what the duplicate looks like in that reduced version. (That‘s one of the beauties of Checkvist: Almost everything is in the textual representation.)