Hey @xYuujii! Welcome to the forums!
It’s because your IA_Crouch_Toggle event is running on a Flip Flop. When you sprint, it sets IsCrouching? to False, which is great. However, the Flip Flop is not triggered, so it’s still going to take the B path before you can activate the A path again.
Take out the flip flop and replace it with a branch!
Use IsCrouching? as the input for the branch, on False use the Crouch path and on True use the UnCrouch path! 
Also, Nightwolf’s suggestions of the Input Actions is a good thing to note, as well. You don’t really need more than one here, you can probably get rid of IA_Crouch completely and use a single Input Action with multiple input styles as shown above!
Let us know if you need more assistance!