Errors adding downloaded transactions to register

I have been having this problem for a while and I haven't been able to find a reference to it anywhere. Perhaps I don't know what to search for.

I am running Quicken Classic Deluxe Version R64.35 on Windows. I have a file with multiple accounts and about 20 years of data input. In the last year or so, I have noticed that when I am going through downloaded transactions to enter them, many of them will work correctly. But then after a while, when I press enter the transaction I am working on will get entered and the next transaction in the downloaded transactions list will get highlighted. But, the info that shows up in a new transaction to adjust in the register is completely different. For example, when working on credit card transactions, the downloaded transaction window will show a recent purchase from Amazon or Jiffy Lube, but what shows up in the register is always a duplicate of a paycheck from my employer from several months ago. The date, payee, amount etc. are completely different from the actual transaction I am working on. In fact the paycheck transaction that is being copied is from a completely different account at a different bank.

If I fail to double check that the register entry actually matches the downloaded transaction and press enter, the wrong information will be entered into the register and labeled as reconciled. Instead of removing the downloaded transaction from the window and moving to the next one down the list as would usually happen, the correct transaction stays in the list as not yet accepted, nothing in the downloaded transactions list is highlighted and the register window moves to a blank transaction as it would when entering a new transaction manually.

If I notice this is happening, I have found that if I click a different transaction in the transaction window, it will load correctly and I can either work on that transaction or click back to the one I was working on to begin with and it will also load correctly. This pattern seems to happen more frequently, the longer I work. Within a session, the wrong transaction that gets copied is always the same. It is always a paycheck from the same employer from several months ago, but it is not the most recent entry from that payee, or even the most recent reconciled check. When I close Quicken and reopen it (usually several weeks or even months later) the pattern will start over It will work fine for a while then start going wrong occasionally, and then more and more frequently.

This does not seem to happen if I edit the previous transaction in the register before hitting enter. Only if I decide the downloaded transaction is correct as is and hit enter directly