Well I can at least address your first question with the information belongs to it's implementation part, even it has considered within development phase which is out of this site's scope.
First, it's pretty easy to find out a client (targeted user here) device's operating system via a server-side programming language. So that you may understand if it's iOS, Android, or Mac/Windows. By this way basically, you may try to warn each of iOS/Android users that they may have an experience of this kind of problems first.
Then additionally, you may make them voluntarily report these kind of issues or try to use any other kind of operating systems or devices (to say web here) to be able to get a better performance.
And also for your second question: I think most of the sites like HackerRank already doing it today like warning their users to use Firefox or Chrome other than the rest, when they want their users to get most benefit out of their applications.