I’m wondering if you have disabled saving the image with a background companion on purpose if no character is chosen? When you select “no character” and select the horse (big companion) you won’t be able to save the image. You can however save the foreground companions (which I really like since I need them in a separate png and not with the main character!) without problems.
The thing is that I could very well use the horse and a few other bg-companions separately but it won’t work without characters. After pressing save it will start to check the license etc and through you back to the main menu.
Btw. this only happens with transparent background (no background selected).