Thank you for signing up to QuickBooks Self-Employed, SarahSignsBSL.
You're probably following the steps in the article about formatting CSV files in Excel to get bank transactions. Therefore, we'll do the other troubleshooting steps to find out if the behavior is caused by random browser issues.
If you haven't done so already, you can sign in to QBSE using a private or incognito browser. This will prevent the reuse of cached data and disable extensions, ensuring that you receive fresh data from Intuit's server when accessing QuickBooks pages.
You're able to upload your transactions without issues, you can clear the cached data. If not, please use a different browser so we'll know if this only happens to the one you use or not.
Let me know how the instructions work for you. Take care and have a good one.