I can also confirm I had issues on my first mission drop in load screen. Me and my friend nearly crashed (froze and hard stuttered for about 5 seconds), and then it started slowly smoothing out. After that, every single drop in load was super smooth, no stutters nor near crashes.

We were both on the slim beta.

My best guess is some kind of first time shader compile for the epic load screen scenery, on top of what is already an intensive process. IIRC, this is when the map is also being generated.