If your course is freezing, crashing or not saving progress, this is likely due to a drop in connection.
Please test your internet connection. Your speed will need to be above 5 Mbps to run the course without issues (Kbps is slower than Mbps).
If your internet speed is above 5 Mbps, there may be issues with your connection dropping, even the fastest of connections can drop for a second or two. It might be worth refreshing the page and trying again.