i have the same problem with my characters cape. It has nothing todo with textures, the whole object (mesh) gets blurred by the motion blur at full strength/velocity all the time when there is just minimal movement on the object. Vertecies with 100 skinned wheight do not get blurred, but if they have anything less they get blurred.- i could not find any fix for this, even reimporting and setting everything up from scratch did not fix it.