You can disable this: when in a lesson, click on the gear in the right upper cormer, then you get some possibilities, among which disabling the automatical marking as known when paging.
I’m having trouble doing this on Android. If I disable ‘mark as known’, skip ahead, and then turn ‘mark as known’ back on, I get sent back to the page I was on when I turned it off, defeating the purpose of paging ahead in the first place. This doesn’t happen on the web. I’m sure it’s not supposed to do that.