The instant brand page uses bookmark links to navigate down the page to the respective letter when an item in the A-Z list is clicked.
On some stores - when doing this the page goes blank instead. This is down to how the URL is being interpreted by the store.
To address this the app has the option to change the URL link from full length (store and page path) paths to short (page path only) length.
Simply change this setting to resolve the issue and click Save