Updating bank transactions, Quick Books seems to be missing roughly 12 months of transactions - both for my chequing account and my credit card account. How to fix this?

You can use MT Online or one of the converter tools (e.g csv2qbo @ $60 one time license) as a workaround.

https://www.moneythumb.com/?ref=110

Hello vandens, 

Welcome to the QuickBooks Community. I'll be happy to provide the info you need so you can move forward with your work. 

In order to keep your transactions up to date, I recommend manually uploading the transactions. After manually uploading you can match your transactions using the steps provided in this article. You also have the option of setting up bank to automatically categorize the transactions from the manual upload. Here's an article with more details on that. In case you come across duplicate transactions, you can delete them by following the steps below:

1. Navigate to the Banking/Transactions menu.
2. Click on the For Review tab.
3. Select the checkbox of the transactions to exclude.
4. Hit Exclude.

Feel free to ask other questions. I'm here to steer you in the right direction.