How come my skills wont strengthen?
I just spent an hour strengthening one, doing it about 3 or 4 times... and when I scroll down, I see that it is not strengthened at all! ... Is this a bug or what? This is on MOBILE by the way.
Sometimes this is caused by a bug.
Then you need to repeat one or more of the lessons instead of strengthening.
The App is bad in strengthen, because of its teaching method "mostly choosing from predefined words" instead of " mostly typing all the words by yourself".
If you like to use the App, just accept this issue.
If you like to learn a language in a more efficient way?
Use Duolingo's web version in the browser of your phone, tablet or Pc (www.duolingo.com)
Log in with the same username and password as in the App.
They just want you to do more exercises so that they can serve you more ad impressions. BTW, you should move your post to the "troubleshooting" forum.