Hello @bdip
Thank you for reaching out to the Community regarding your issue, although I am sorry to hear that you are experiencing issues with your 401k. Did all of the transactions duplicate or are the specific entries that are causing the issue? Another thing is if the amount inside of the account is duplicated it could also be the cash balance is the same as the account balance if you can't find duplicate transactions.
Another option could be to try loading a backup and updating your transactions as well but I would wait first to see if we can find the culprit of the issue before attempting this.
Once you get a chance to try these steps, please let us know what you find. From there we'll better understand our next steps/options.
Thanks,
Quicken Francisco