duolingo seems to be having problems updating progress when you are strengthening a lesson learned
I noticed it too. I've done 4 lessons today (None that required strengthen). Redoing the lesson, Strengthening without and with a timer will only refresh a few words. My first time no word was refreshed. 4 Lesson, 13 words refreshed. I'm doing this on my computer too. I typically have at least 13 words refresh in a lesson.