"Fit to frame" size not kept after closing

Hello. I use Framemaker 2019 to write user manuals for work.

Since I use a large amount of photos and other images, I would love to use the "Fit to frame" option when I import something into an anchored frame. Unfortunately it only works until I close the document.

As I import them and fit them, the picture looks good. But when I open the document a second time (after saving it and closing it), all the images have returned to their original import size (usually 300 DPI), forcing me to resize them all manually.

What am I doing wrong? Why do they all get small again?
This only happens with the "fit to frame" option, not with manual resizing.