I keep this thread up to date, in case of someone else have this bug issue : The problem still appears on 5.2.2p3. (I noticed in 5.2.2p3 a LogStringToConsole line which takes some times too. Don't you forget to remove one of your debug log guys ?) BUT our studio was forced to move on 5.2, because we absolutly need asset bundle manager. So, I spent some times to find a solution for these huge freeze aaaand I found one. I put Text component with every font I use in my game with every caracters of my keyboard, set best fit from 0 to 100 size, I displayed them on splash screen, first scene on first frame and tada! No problem. Because I think Unity put them on cache and my UI doesn't freeze any more. Some UI will freeze, may be I miss some special caracters, so I simply display the UI on splash too with the other fonts, and it works. So it's a dirty fix but Unity team, even if they are doing their best, aren't fix this problem yet and this is the only solution I found so far.