Some users can’t type a ‘d’, erratic error

I have had two users who had a problem with being unable to type the ‘d’ when trying to fill out an application using Everest forms. But I also had trouble with the ‘d’ when replying to a comment, so I had to reword everything to be d-less as did the two users, so it’s not just a problem with the form. But although I have used the same iPad for everything related to the site, that is the only time I had problems. And no other users have had a problem when filling the form. How can this be? It’s just so bizarre and seemingly random. Thanks for any insight.