The errors usually occurs when trying to import the animation from the native FBX The import sees the rig but not the animation take of the animation your trying to import. Example you can have one character set up in MotionBuilder but 100 takes assigned to the character track so when you try to import the raw FBX into UE4 it finds the character track but not the animation track from the 100 that you want to import and get the “Mesh contains Root bone as root but animation doesn’t contain the root track” error.
Long way of saying UE4 can not import motion data saved as a raw MotionBuilder FBX file no more than it can import a raw .max file from 3ds Max as there is no way to select a take from the format from the X number of tracks available.
But.
If you add a character rig you can use the save animation feature from the character control and select which plotted take you want exported as an individual clip based on the name of the take which can be imported into UE4 as part of a batch process that only contains the root track that excludes the character rig and extensions.