On rare occasions, you may find yourself in a situation where you'll watch a whole video lesson through, go to the next lesson, and find the previous lesson wasn't marked as completed. This can happen for a number of reasons, including glitches with your browser, server glitches, etc.
However, this can be easily remedied by manually toggling the lesson completion option via the instructions below.
Zenva Academy Website
1) Manually select the lesson having issues from the course home page.
2) Locate the Lesson Completed option under the video and toggle it to On (slider will be to the right as shown below)
1) Manually select the lesson having issues from the course home page
2) Locate the Mark As Completed button and press it (it should say Completed when toggled correctly).