Thanks for joining us here in the Community, Simonscw.
I want to make sure you're able to view updated bank transactions in your QuickBooks Online account.
As an initial troubleshooting step I recommend clearing the browser cache first. The cache is in place to collect frequently used data to make loading web pages quicker and easier. If it becomes too full it can potentially cause certain viewing and performance errors. Clearing the cache will remove anything that's preventing the transactions to update as well as the error. Here's how to get this done in Chrome for example:
1. At the top right, click More (three vertical dots).
2. Click More tools and then Clear browsing data.
3. At the top, choose a time range. To delete everything, select All time.
4. Check the boxes next to "Cookies and other site data" and "Cached images and files."
5. Click Clear data.
The following article provides similar steps for other browsers: Clear cache and cookies to fix issues when using QuickBooks Online
Please give this a try and let me know if you're able to update the banking page afterward. I'll be here if you have any other questions.