That bug fix would have been integrated into Totara 2.2.13 so I don't think that's the problem.

It sounds like the permissions aren't quite set up right. The function that controls access is wiki_user_can_view() in mod/wiki/locallib.php.

Are you using groups in the course? I assume the wiki mode is set to "Collaborative" rather than "Individual"? Are you sure the students have the mod/wiki:viewpage capability in the module's context?

Simon