If you can predictably recreate the problem, I would clone the page and use the clone as a testing environment where you go through feature by feature and delete each feature and test until the duplication goes away.

Skuidward is right. This calls for some advanced debugging. A few tips, assuming you can actually make a page reproduce the problem.

1. Look at the model data (in the devleoper console) and determine if the duplicated data is actually present in the model, or just showing in the component.


2. The usual suspects in cases like this is Javascript you have added to the page, or Back End Apex that is getting triggered unexpectedly.


3. When you start testing features added to see where the breakage happens, make liberal use of the “revisions” feature to set a “good working page” and then revise and revise. That way you can easilty get back to something that was working, or at least familiar.

Good luck!