Are you using blendspace for walking? Maybe this is just a theory but when you mix 2 animations (walk, run/sprint) and you have notifiers in both animations they will trigger when blended between.
Try to remove notifications from run (for example) and test it.
Also, use print in notifier event to debug. Make one step and see how many times it will output. I think I have similiar problem long time ago (could not remember what I did) and footsteps are almost always echoing (like trigger twice in short time for one step).
If all of these does not help remove all notifiers in animation, add one by one and always test when you add new notifier (so you can potencially notice where’s the problem).