All the icons on every widget appear as a question mark whenever I try to edit them and put them on the home screen. How do I fix this?

I have seen this happen before. It's when kustom can not find the icons that are being displayed in the widget. So either the files got moved or they dont exist. I'm guessing that they weren't included in the preset which happens a lot. Especially if the icons are "paid" from the play store or wherever. So your best bet is to just add your own icons. Or if you don't want to change the ones that are in the widget, you'll need to find out what pack they are from and download it and add the icons that way