It's not clear whether this 'duplicate' security keeps reappearing. If so, you need to resolve the reason first. Normally this is where the CUSIP of the security has been given two names by your bank. Toolbox extension has a feature where you can view your hidden CUSIP settings.. Look here first. Also, if you have Menu/Window/Open Console open whilst you download from bank, then you will also see in the data the CUSIP being sent.
Toolbox can also tell you where a security or currency is being used.
I would certainly start by getting rid of the duplicate currency (after carefully removing etc the txns within it).
Then I would let us know about the CUSIP?
FYI Toolbox has a merge duplicate securities function... Always Backup first.. Ensure you select the security that you need to keep using for download txns as the new master. There are certain rules before Toolbox will match and allow you to proceed, it will tell you about these.. But I would only do this once you have fixed the above first....