Having an Item Frame and Comparator in a different chunk (facing east or south) will cause the item frame and item to dupe when chunk is unloaded then reloaded.
This also dupes entities. If they stand where the Item Frame will be.
Pictures attached show this a bit better.
This video also explains it better https://www.youtube.com/watch?v=GviRuuue35U
Dupe of MC-51610