I was currently adding movies to my catalog, almost to the point of having 1600 movies. However, I have checked now, and its like more than 100 movies have disappeared, but on the other hand on the folder mode they show that 1600 number. Why is plex not showing the movies on the picture mode?
Wild guess (without further details):
you have a bunch of items that have their own folders but are considered to be duplicates (different versions of the same movie).
Try filtering the library view by duplicates to see if that adds up to approx. 144 items.