If there is a course that has self enrolment turned off, but has something like the Auto enrol plugin enabled. In the web version of Moodle, if a student visits the category page that course sits in, the course appears as expected, and can be clicked on to access.

However - the same course when viewed from the same category page on the mobile app, will show a padlock icon and the message when hovered of 'You cannot enrol yourself in this course'. This is confusing (and bad accessibility) for the learners, who don't realise that they can still click on the course to go into it (and be enrolled on it via the autoenrol plugin).