I save this AE document to a .PDF file then I import it back into AE as a base document, the number of elements is different. Is this a bug or a software necessity?
Original document :

Imported .PDF document.... Why are these empty elements?,They were two photos in a placement element (Grid) originally.

Yves Crausaz, Suisse, retraité actif dans le monde de la photo et des arts graphiques.