At the end of the user import stage, I get told "The following users could not be imported due to errors". It then lists about seven users who it was unable to import (I assume due to characters in their username, like commas). But I am not given any option to offer an alternative username.
I saw a similar thread, here, which suggested there should be a text box for me to correct them, but I cannot see this. I don't think there is one in my case (I checked using Inspect Element). The only option, at the end of the list of usernames, is "Import Users".