I have Quickbooks Online and when I manually upload a bank statement in .QBO format, there are always some random transactions missing, why?

Missing transactions could be due to incorrect file formatting or automatic categorization, Barb.
 

To begin, please ensure that these transactions are included in your CSV file. If they are present, the next step is to check the file format of those missing transactions, since an incorrect file format will exclude them from being imported.
 

If the file format is correct, it's possible that you have set up bank rules, which automatically categorize your bank transactions:
 

1. Navigate to the Transactions, then Bank Transactions.
2. Go to the Categorized tab, then try to locate those transactions.
3. If the transactions are there, click Undo to put them back in the For Review tab. 
   

However, if everything's fine after checking all these factors and the issue persists, it's best to contact our phone support for further investigation. They have access to specialized tools that allow them to conduct a thorough investigation of any unusual behavior with your bank feeds and provide you with tailored assistance.
 
Additionally, you might want to reconcile your account to ensure your QBO transactions match your bank statement.

Furthermore, you may want to explore QuickBooks Live Bookkeeping to streamline your accounting processes, ensure accuracy in your financial records, and provide expert support, allowing you to focus more on growing your business.

I'll be around if you have additional questions about managing your bank transactions in QBO. Have a good one.