See following two images:
https://photos.app.goo.gl/s1jDu1fRapzD14rD6
https://photos.app.goo.gl/s1232pwEtRBwLnLx7

In image 1, "All episodes" is selected and podcast date is correct.
In image 2, "My episodes" is selected and podcast date is incorrect. And it seems this is the date SmartPlay uses, because this episode should be recognised by SmartPlay as the oldest unplayed, but it isn't recognised as such.