Retrieving the course users details has a big impact on performance

This issue only needs to be tested in 1 OS. You will have to use the DevTools to inspect Network requests. Install the app in the device and login as a teacher in master site. Go to MM Dev Course > Forum and enable download options. Open the Dev Tools and clear the network requests. Download a forum with ratings enabled. Check that there are no WS requests to user profile or ratings. Once done, go offline and open the forum. Check that you can see the user's avatars. Try to view the list of ratings of a forum post (clicking the average of ratings). Check that you get a connection error. Now go the Glossary section. Go online, clear network requests and download the glossary "Glossary (browseable by author and date)". Check that there are no WS requests to user profile or ratings. Once done, go offline and open the glossary. Check that you can see the user's avatars (e.g. in the "New 3.6.1" entry). Now go to the Feedback section. Go online, clear network requests and download the feedback "Not-anonymous feedback with multiple attempts numbered questions". Check that there are no WS requests to user profile. Once done, go offline, open the feedback and go to "Show non-respondents". Check that you can see the names of the users, but not their avatar (it's the default image). Now go to the dattabase section. Go online, clear network requests and download a database with ratings enabled. Check that there are no WS requests to ratings.