Disappearing preview when making a lattice grid

I am trying to make a lattice grid using overlapping horizontal and vertical rectangles, all goes well until I get to a certain number (19), but when I add a 20th or more, the preview disappears. Is this a bug or a limitation? I would send a movie, but can’t work out how to attach it, or if I can. If not, will find an alternative

Can you send me the file? Send a link to the file in a private message.

Can you try the latest cutting edge version?