My experience with Unlimited status

[Hile]

Sounds to me like your computer is way way too slow to play this game. Lower all your video options to lowest settings. It may help a bit. I hope you're at least using a broadband connection.

For the mobs that appear out of nowhere, yes some are hidden like dread scorpians. If you can have a high enough graphic setting, you'll see a green mist appear just before they spawn.

One thing they did do was take out some of the high level mobs that were hanging out near the towns. There was a grenadier hidden behind the houses in Tortuga. If you got anywhere near him, he'd pulverize you fast and you wouldn't know where it was coming from. Also the huge alligators in Cuba are gone. I'm sure that was quite a daring run to Tia Dalma for a low level.

Another thing if you aggro a mob and run off they can still get some swipes in before you get far enough away, especially if they have ranged weapons. I've had those fly traps nail me from quite a distance. So to run away you really need to get very far away.