You don't need to use the Game Lab to get this achievement. Just go into the Custom Match menu and set session type to Game Lab and Matchmaking to Public, then wait to find a game. I started with an empty lobby, but there were enough players to start a game within a minute or so. Once the match starts just stay until the end and the achievement will unlock.
You need to be in the match from the beginning to get the achievement (thanks to PHANT0M LEGEND for confirming this), so if you are dropped into a game in progress be prepared to stay on for another match afterwards. This achievement seems to be a little buggy (details below) so you may need to play a few matches before it unlocks.
According to FuzzedUpCookie if you fail to find a match on your initial search you must back out and begin a new search for a Game Lab match. This is because selecting the search again option results in being put in a normal public match instead of staying in Game Lab.
Several people have commented that the achievement didn't unlock immediately after they followed this method. destinee ehgc described playing a number of matches where a warning about server problems briefly flashed up without gameplay being interrupted, and says that the achievement unlocked after the first match where the warning didn't appear. I MR FLASH I also described having to play several matches before the achievement unlocked, but with no indication of network issues.
Patience seems to be the main fix for getting this to unlock. If you continue to have problems I suggest contacting Ubisoft:
- Uplay account holders can file a support ticket at https://support.ubi.com
- You can report problems on the official technical support forum at http://forums.ubi.com/forumdisplay.php/189-AC-Community-Tech...