Images move by themselves

Images move by themselves

In a zohosheet file, I have pasted a lot of images. It is a project tracking sheet, and having images of the products is a GREAT HELP!
 
However, some users complain that all of a sudden, some of the images just move around in the sheet and are no longer locked in their original cells.
 
Does anyone have any idea what is causing this?
 
A major headache right now!
 
I can share the file with customer support if that is needed.
Thanks,