Try logging in in a private window on the browser (ctrl + shift + n in Brave). It’s more than likely messed up cache if nothing has changed on your device or network. If the private window works then it is just cache issues and you can clear it if not done already of just wait it out to fix itself. Unless of course it’s a Trackt UI issue but I doubts it that.
It wouldn’t have anything to do with most artwork coming from TMDb? They have backdrops, posters and logos but don’t have banners, so Trakt is filling in with placeholders?
Yes, that is exactly my problem. In the past there were actual show banner and sometimes even movie banner artworks in banner mode. Now they are not showing anymore.