Oh okay, yea the Standard FP stuff actually accounts for that, but it has some "advanced" features that really don't do it any favors. On the bright side, this means you should mostly be able to fix the issue by going to your Input Axis settings and changing the Horizontal and Vertical Gravity from 3 to something like 100. The sensitivity controls how fast the axis lerps towards 1, and the gravity controls how fast the axis lerps toward 0. When you start walking with this controller the speed is immediate, so the sensitivity is fine. But when you let go it has a curve multiplier that it uses, which keeps full speed for half of the lerp. By changing the gravity to 100, this will speed up the process and the character will come to a smoother stop.

I highly recommend at least trying it out, it would just be changing the axis gravity; and if you don't like it, put it back to 3. But I guarantee it will be an improvement :)