The reason you’re getting duplicates in this scenario is that the Tiller Money Feeds add-on writes the data validation rule back into those columns after it feeds new data in, but since it can’t find the Statements sheet it crashes on the re-writing the rule and then it doesn’t know where it left off adding transactions (in come the duplicates).
The fix for now is to remove the Statements column from your Transactions sheet (right click the column header to delete it) and then the updates will stop crashing and causing duplicates.
You can try using the Duplicates Manager from Tiller Labs to correct the existing duplicates.