Falling endings are not usually attack problems
Many singers start on pitch and fall only in the last second. Isolate the ending or the issue stays hidden.
When airflow lets go, pitch can fall
When support lets go at the end, tone thins and pitch often slides down. The goal is supported release, not holding tension.
Sing straight before adding style
If endings are unstable, do not rush vibrato, turns, or longer holds. Stabilize a straight ending first.