I've played for a bit, and this is what I see in my logs:
Code:
[23:46:24] [Server thread/DEBUG] [FML/]: The world 241f1cbb (Trajectory_TheWorldForMe) may have leaked: seen 415 times.
[23:46:24] [Server thread/DEBUG] [FML/]: The world 48bb777e (Trajectory_TheWorldForMe) may have leaked: seen 415 times.
[23:46:24] [Server thread/DEBUG] [FML/]: The world 38140f5e (Trajectory_TheWorldForMe) may have leaked: seen 415 times.
[23:46:24] [Server thread/DEBUG] [FML/]: The world 32f1ee70 (Trajectory_TheWorldForMe) may have leaked: seen 415 times
[23:46:24] [Server thread/DEBUG] [FML/]: The world 2df4e30e (Trajectory_TheWorldForMe) may have leaked: seen 415 times.
[23:46:24] [Server thread/DEBUG] [FML/]: The world 48e309fd (Trajectory_TheWorldForMe) may have leaked: seen 415 times.
[23:46:24] [Server thread/DEBUG] [FML/]: The world 7eb23601 (Trajectory_TheWorldForMe) may have leaked: seen 415 times.
[23:46:24] [Server thread/DEBUG] [FML/]: The world 52a48324 (Trajectory_TheWorldForMe) may have leaked: seen 415 times.
There's a whole lot of such stuff, and when it gets to 500ish numbers, Minecraft just hangs.
Nothing can be done from this state but killing MC with kill -9.
Edit: out of logs I've found (not fml-client-latest) that the freeze has something to do with my graphic card drivers, and the logs are just a coincidence.
Probably Optifine going nuts.
yep actually the option should be named "AnnoyingAchievements"