Your walking and jumping animations are trying to play at the same time because you aren't properly checking if your player is on the ground or not. Adding sub-events with no actions doesn't help anything..
You want to change them to something like
+Player is on ground
(sub event) Player is Walking : Set animation to walking
(sub event) Player is NOT Walking : Set animation to Standing/Idle/Whatever
+Player is NOT on ground
(sub event) Player is Jumping : Set animation to Jumping
(sub event) Player is Falling : Set animation to Falling