can you tell us a bit more about it, since this is not normal behaviour. It's possible you have a faulty phone, but if you've tried modifying the software (or bought it from someone who had done that), or are running the Android P beta, or anything like that, then that could be relevant.
When you say apps "disappear" do you mean they are no longer in the app drawer (when you swipe up from the bottom of the screen, if you are using the default "launcher", i.e. desktop app), or just that they've disappeared from your homescreen? If you go into Settings > Apps are they still there? It might be that if the phone was unlocked in a pocket they've been moved or removed accidentally by the screen rubbing against your leg or something.
"icon" was actually the correct word: a "widget" is a tile you place on the desktop that displays live information, such as a clock weather forecast, music controls, calendar display, etc.