Hello,
The RadEditor's Design View became unusable in the latest Chrome Beta version (Version 73.0.3683.27). It is still working correctly on the latest stable Chrome 72, so I'm not sure if it is a problem that needs to be resolved on Chrome's end, just figured it'll be helpful to send this in as well.
The HTML view still works, but switching back to Design causes an exception (attached). This is also directly off of the demo page, so it doesn't look like implementation is a factor.