When i zoom in everything disappears. Really need help with this

Im trying to do some pixel art and have the cavas set to 40x40px at 72dpi.  Whenever i zoom into the cavnas the pixels in the middle of the screen turn white.  In the video i have filled the canvas with black and it works but when i zoom in it gets messed up, its the same when i try using the brush tool.

would greatly appreaciate some help on what to do here.  i have looked it up but nobody else seems to have this problem.