My new video explains the most common reasons why singers fall or sing flat (beneath pitch) which breaks down to: (1) Not enough breath support, or, more commonly, (2) not enough space in the face and mouth to allow the pitch to resonate.
Staying on pitch for singing requires also that you anticipate jumps in notes, like ascending intervals, and it's important to get your "landing gear" out and ready BEFORE you land (sing a note).
If you've been told you have "pitch problems," don't worry. Learning how to stay on pitch is simpler than you think. Learning how not to sing flat takes some practice so your cords have more control, but it also is a mental process. And the more you can utilize these mental cues, the better pitch you will have!
Hope this video is helpful!