Animation flickering

Does it help if you change those bottom four events to these?

Player Platform speed = 0

-----> Set animation to "Default"

-----> Set run to 0

Else

-----> Set animation to "a1"

-----> Set run to 1

EDIT: You might need add an inverted Player Is playing "a1" to the Else statement, so that it only changes the animation to a1 if it's not playing already. This will stop it from starting over infinitely.