Random crash and/or freeze

The game frequently crash and/or freeze for no reasons ; this happens especially when I play in multiplayer. I didn't spotted any patterns, the game just suddenly freeze for 15 - 30 seconds, then I see I a "loading" screen (the one with the two cogs) for another 10-15 seconds before being abble to play again. Sometime, the freeze don't stop, and I have to force quit the game.

This is particularly frustrating when it happens in Chaos' Trial and other bosses...