Hmm maybe some settings got messed up. You can try to clear your browser's localStorage like, for example, described here:
https://www.leadshook.com/help/how-to-clear-local-storage-in-google-chrome-brows...
if the F12 key does not work you can also open the console via the menu button (the one with the three dots) in the upper right corner and then going to "more tools" -> "developer tools".
This will probably also delete your save games though.