Button 3:
It appears that you’re missing one more “hide” for image 4.
You command a “show” but not a “hide.”
When you click button 3, you command a SHOW which is immediately followed by a HIDE. The HIDE gets executed while the SHOW is still being processed (fading). My guess is that the HIDE routine fails because the SHOW routine is still busy doing as commanded and it maintains control of the image item long enough to make the HIDE routine fail/miss.
This is evident when you click button 3 a second time - since the images are all showing, the SHOW routine has no effect or finishes quickly enough, so that now the HIDE routines can fire and hide the images - except for #4, because you’re missing a command to hide it.