It's because game randomly generates stats for every item. There is NO really unique gear, no reason to seek for such chests, since they all give you the same. Just some of the has higher "item level".
Here is what you need to do:
1. Save before chest
2. Load.
3. Open and check if the gear is ok. If it's not:
4. Load
5. Open and check if the gear is ok. If it's not:
...
...
...
