Just want to add that I, too, am experiencing the issue of not being able to place my cursor in the necessary place. Not only am I unable to click to place the cursor, but am also unable to get to the right spot with the arrow keys. The editor simply won’t let me place the cursor where I need it.
How, then, am I able to finish the challenges? Well, if I use random clicks mixed with random arrow keys, I eventually gain access to the spot I need to add text. I can’t tell you exactly what click/arrow combination works, but I can confirm that there seems to be an issue with the editor. Sounds like the same issue described here.
I’m using Chrome v61. If it would be best to contact/work with someone in particular on this issue, please let me know; I’ll help further if I can.