It could happen that some chapters have an asterisk next to the title, like this:
Or a warning triangle, like this:
These only show up if the title of that package/page/chapter/etc is not translated into the profile language the user has selected at that moment.
It is not possible to hide the asterisk/warning triangle from students. The only way to remove it is to change the titles to the particular language that students are using.
To change the titles, go to Teacher, and then to Course material.
Right-click on the chapter that has the asterisk, and click on "Rename".
Here you can translate the chapter name, or just delete the asterisk if the translation is not needed.