I found this solution by accident, trying everything and everything on my personal pc. It worked for me and a bunch of people in my unit.
Go to the lesson that is not updating, when the lesson window pops up it might ask you to fast forward to your most recent point. Click "NO". Start the lesson from the beginning, as you click Next through the slides it will act differently, skipping lesson sections that apparently show up in the system as completed by you. When you have completed the lesson to the very end, click on the prompt that tells you to go ahead and exit the lesson window. When you exit the lesson this time, it should refresh your lessons and show it as completed. Do this for all of the lessons that you have completed but still show up as incomplete.
I hope this helps!