why did my icons disappear on my for my galaxy s4

[AC Question]

the icons for my sd card apps are gone from the home screen

 

[SpookDroid]

If you have apps installed to your SD Card and your phone unmounts/remounts the card at boot, that's why you lose homescreen icons and/or widgets. It could also mean your SD Card is beginning to fail, which is why I wouldn't recommend storing important information or apps on SD Cards.