Most likely reason could be that your app session expired because you have been logged in for a long time.
If that's not the case then please open the developer tab of your browser by right-clicking on the page and selecting "inspect element", and then open the "console" tab.
Take a screenshot and send it to us and we will resolve your issue as soon as we can. If you don’t use any tools for screenshots or videos, try the free Nimbus Google Chrome extension.
You can send us the screenshot via chat or email firstname.lastname@example.org