Chaosmancer
Legend
Butting in, the servant is described as a shapeless magical force. It almost certainly doesn't have any weight (unless you decide that all magical force creations, including Bigby's hands and Tenser's disks have weight as well), so it's not going to trigger pressure plates or pit traps. Because it's shapeless, it will "flow" around any tripwires, levers, or other triggers. At least not on its own. You could likely direct it to do so, but that means you'd have to know where the trap is, and the trap would have to be sensitive enough to be triggered by a Strength 2 entity (30 pounds of force).
Weight is pressure. Per the original example, the Unseen servant is applying pressure to the floor and walls. So it certainly should trigger any pressure plate or pit trap that it presses against.
If it "flows" around things, then it can't do what it does as a servant, like lifting up a glass or picking up forks. Heck, the thing can sew, so it should surely be solid enough to pull against a trip wire, and it can easily throw levers, that's a job a human servant can do.
And 2 strength is 60 lbs. It can pull, lift or drag 30 times strength.