May I know what specific error you've encountered? Is the VAT/Taxes page isn't displaying anything? If so, it's possible that the browser you're using has some issues. To verify, please log in using an incognito window and check if the VAT/Taxes page is working already.
Also, it's best to clear the cache as it's causes unusual behavior in QuickBooks Online. If you have other browser available, you can use it to do your other tasks. Just make sure that it's updated.