When did your MuleSoft.U session end? Note that course videos expire 3 months after the completion of your free, self-study course. If you would like to be able to review them again, please enroll for the next course session.
In addition, if you've signed up multiple times for MuleSoft.U - it can take a day for all the modules to appear refreshed in your account. While content does get added every week on Wednesdays to the course, for folks who've taken the class before it might be better to shift to Thursday at 9 am Pacific Time, to give the script time to repopulate your account.
If you are still having issues, submit a request here.