Trying to sync my account, it is missing 4 months of transactions. I tried importing manually. Quickbooks say's they are duplicates, but they do not show.

Let's find and add those missing bank transactions, @dboy360-gmail-co.

Can you tell me more about the bank that you're having these missing transactions? That'll help us check to see if there's an ongoing issue with it.

Since the system has triggered duplicate transactions, try to check these transactions from your Transactions tab.

Here's how:

1. Go to the Transactions tab.
2. Set the Type to All, the bank, and then the date.

Once confirmed that there are no any transactions, try to check if the CSV file has the right format and you only add those transactions that are missing from the account. 
 

It should be either 3 column format or a 4 column format. You can refer to this screenshot for more information:

You can check these articles for more information: Manually import transactions into QuickBooks Self-Employed.

Here's also a guide to help you add those transactions manually in QBSE: Manually add transactions in QuickBooks Self-Employed.

Let me know if you need further help with adding those missing transactions. I'm always here to help you out. Take care and have a wonderful day!