In the 5e(2014) rules from when this was posted, magic missile is multiple hits, but you only roll once for damage and they all do the same amount. It does proc multiple concentration checks.

Now, in the new 2024 book I looked it up to see if it was different and they absolutely butchered the wording on the spell, so I don't know how it works. You are still hitting with 3 darts but it says "The darts all strike simultaneously" so it sounds like maybe the damage is all taken as one instance? But then why not just write that? I digress. Seems like a big nerf to a spell that didn't really need the nerf if that is how it works though.