On the upper right corner of the viewer there is a small dropdown menu. This is a draw timeout in seconds. Its purpose is not to slow you down in case you don’t want to wait for the complete toolpaths to display or run the application on an old computer. Try increasing that.
I’ve seen what you describe on my RPI, so I leave the draw timeout higher. On my office workstation it draws a lot faster.
If this does not solve it for you, look here to see if it has been mentioned and, if not, open an issue.