The attached asset (including animation) takes 9 minutes to import in 4.10, where it takes 42 seconds in 4.8 and 4.9.
You don't really notice this until you start to get up to larger assets or long animations (this one is 1700 frames), but could also affect the process of importing multiple FBX files at once.
1. Download the attached fbx
2. Open a 4.10 project
3. Import the FBX
4. In FBX Import Options, but sure to check "Import Animations"
Result: Wait 9 minutes for import
Expected: Takes approx. 42 seconds
There's no existing public thread on this issue, so head over toAnswerHub just mention UE-24293 in the post.