This issue usually occurs if your browser cache is full.
To resolve this, please look to clear your cache as follows:
1. Click your name on the top right of the screen.
2. Select Preferences from the drop-down menu.
3. From the Preferences page, click System Settings on the right.
4. Then click the Reset Cache button.
5. A popup will come up on the of the screen confirming "Your cache has been reset".
6. Press Ctrl + F5 on your keyboard to refresh the page for Windows or Command + R for Mac.