A change was made to AActor.GetComponents which appends the results instead of resetting the output array. This seems to only impact 2 places in the code, and has a big side effect in the texture streaming level initialization. The in-game texture streaming behavior is not affected though.
The fix for this is very simple and is in Shelf 3487210
Load map stalls when building the texture streaming component data.
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-46004 in the post.