You do not make clear if they are disappearing in screen when the application runs or when you open the layout designer again.
If it is the first maybe some kind of script in the layout designer script or you may have designed it for a specific variant? An other thing that happened to me in runtime is that I copied a layout from B4A to B4i and obviously the images did not have the corresponding image files available, so what happened was that I thought they were gone but they were there with no image to show...
If it is the second maybe a synchronization in OneDrive, Google Drive, Dropbox, or what else with a colleague of yours in your work?