An author once reported to us that they were unable to see a cursor when working in our online editor, in our Browser writing mode.

In this case, the problem was they were using a colour changing app to make websites more readable. It was changing the cursor colour so it was invisible.

The solution in this case is to adjust the settings in the app so the cursor is visible, or disable the app on Leanpub, if that is an available option for you.