OK, so on this you do a scale up to D#4 and E4. You are successful when you open up your lips to an ah vowel, but when you transition to LAH, you have less support, which makes it sound weaker, and it then falls flat.
Can you hear that when you listen to this track?
You are not maintaining the proper pressure on the note after you get into the LAH. Listen to the difference in your voice when you open up. You're not supporting those notes, when opened. Remember, it takes more support when moving higher.