I just discovered that there is an issue with the latest update on devices with insider fast builds of Windows 10. The affected version number of Elllo is v3.0.16, and Windows 10 build 15047. The issue is that message bubbles appear empty for both dialogue and video lessons.
The good news is that I already submitted an update for this issue.
I encourage you to pause the current update, and wait for v3.0.17 if you are on insider fast. Sorry for any inconveniences it may cause, and thanks for your patience.