how are your conditions set up?
if i had to guess, you are having the jump animation begin playing while the jump button is down; like so:
"[jump key] is down ---> play animation (from beginning)".
if this is the case, the animation is starting from the top 60 times a second while the jump key is down, & as consequence you are only seeing the first frame; there are many solutions, but here are a couple basic ones:
1. change "[jump key] is down ---> play animation (from beginning)" to "[jump key] pressed ---> play animation (from beginning)
2. add a "trigger once while true" condition to "[jump key] is down ---> play animation (from beginning)" condition
these both accomplish the same task, but option 1 is much better practice.
hope that helps