Problem with "Open next lesson in course"

I just finished this Romanian lesson: Login - LingQ. It is nr. XVI, and it is followed by lesson XVII, of course. However, when I click on “Open next lesson in course” (either from the dropdown or from the “i” pane), I am taken to lesson XX. Three lessons are skipped. Can you please check what’s wrong with that course?
Thank you and happy new year!

@mikebond - I checked the course and it actually looks like this is the next lesson in the course. Perhaps the course has multiple chapters in a single lesson?

No Alex, I have read the whole lesson 16 and it is just that. If I open it in the “edit mode” I see the correct progression: lessons 17, 18 and 19 come after lesson 16 and before lesson 20. Have you had a look at this? This is the “edit mode” url: Login - LingQ.

Oh, I see the problem now: those lessons are private! I will ask Steve, then, since he is the provider.