If the app is showing the spinning/loading symbol endlessly, chances are high that your browser cache is too full. The more symbols and uploaded elements you use, the more resources Flag Creator needs from your browser.

Please clear your browser cache to free space from temporarily saved files to get Flag Creator running again.

You can try to load Flag Creator in an inkognito tab. This way, the browser does not use any old cache. If Flag Creator works fine in an inkognito tab, the browser cache is to crowded.

You can find a great manual on how to clear the cache of different browsers here: https://its.uiowa.edu/support/article/719