What is the security involved here, and what financial institution? Maybe something happened with that security in the real world on that date?
Reverting to a backup as of 5/23 would "undo" what happened here and NOT allowing downloads to enter your Transaction List (register) automatically would prevent this from happening again.
Vanguard uses Direct Connect for downloading, typically a very reliable method, and having only one Account affected surprises me and I wouldn't think an update would work for other Vanguard Accounts but not that one.
Given that the problem was fairly recent then using a 5/23 backup and trying again would seem to be the best answer here. I would make sure automatic entry is OFF and try again. If the same problem pops up then there might be some damage to the data base itself.
Automatic entry bypasses the "Downloaded Transactions" window below the Transaction List and, instead, immediately places each transaction into the Transaction List, not allowing you to judge whether the entry is correct or not. If it's down in the Downloaded Transaction window that gives you a chance to asses each entry and either accept it, or delete it.
The theory here (as I understand it, having never turned Automatic entry on), is that each automatically entered transaction is somehow identified so that you can review each transaction right there in the Transaction List and make your judgement as to keeping it or deleting it or, I suppose, editing it. The problem is that you get used to NOT reviewing them as you should, leaving you to catch a problem or error somewhere down the road.
You turn it off by opening the Account Details screen, clicking on the Online Services tab, then clicking on the blue "Automatic entry is:" text and making sure it's "off."
Did Vanguard maybe switch you to a Brokerage account from a regular mutual fund account? They have been transitioning people.
