If you experience a black screen when you start a training session, then it can be caused by one of three options:

Video file has been corrupted:

When your internet is unstable, the video file can become corrupted during the download. To fix it, go to ‘My Rides’ and delete the ride, and download it again.

Missing 2013 C++ Redistributable x86:

The C++ Redistributable is pre-installed on most PCs, but sometimes, it is not. If the C++ Redistributable isn’t installed, you will experience a black screen. You can download the redistributable from here.

A memory leak

The video component used has a memory leak. Close the app and start over.