making movies with avifile and addframe produces black screen in half of the movie

Hello there!

I would very much appreciate some help with a movie I am making from my simulation results. Generally, the code is like this:

clear all; clc;
aviobj=avifile('movie.avi','fps',5);
img = figure(); 
ax = axes('parent',img);
hold(ax,'all');
set(ax,'XLim',[0 300]);
set(ax,'YLim',[0 300]);
for i=1:288
   pl = plot(i,i,'parent',ax);
   aviobj = addframe(aviobj,getframe(img));
   delete(pl);
end
aviobj = close(aviobj);
close all;

Obviously, the pictures in it are more complex but this is the principle.

This works well, except: When looking at the movie, the second half of the movie is just a black screen.

What could be the problem here?

Thank you very much for your help!

Anna