No this is not a change.
I can see the "Ajax course" was disabled, so, I unchecked it. So, now when students click on next/prev unit you'll see a loading icon and the content will change inside the course. Since you were not using Visual composer, this setting can be safely turned off, it is faster and enhances the course taking process.
Students not able to view the unit may be possible because the drip feed tracks the last unit "view" timestamp and if they did not view the previous unit, it would not take them to the next unit.
However, from your video the issue seems to be connected with the Non-ajax unit loading, so the issue should be resolved by turning off this setting now.