The "Next" button is not going to the next section

I've been testing out courses and noticed the "Next >>>" button doesn't go to the next unit after finishing all of the sections for the current unit.

Here is a quick video of the issue: https://cl.ly/3Y2G1R0R3V2i

After clicking, it goes from the 1st section to the second one. However, it won't go past the 2nd section, which is the last of the unit.

I deactivated all of the plugins to see if there was a conflict. I've turned on the WPMU support if you'd like to access the site. Thanks for taking a look!