To ensure that I'm on the same page, may I know which specific bank you're using? Any additional information will help me provide the best resolution.
In the meantime, try logging into your QuickBooks Online (QBO) account using a private browser (incognito). There are times that the browser is full of frequently accessed page resources, causing some unusual responses.
If it's successful, go back to your default browser and perform a clear cache. Every so often the cache becomes overwhelmed with older data which can potentially cause viewing and performance issues. Clearing it will refresh the system, and you'll be able to work with a clean slate. However, if the issue persists, try using other supported browsers.
Reach out to me in the comment section below if you have any other issues or concerns. I'm always here to help. Have a great day!