Elaborate on what you mean by "not working". Does the app not open when you press the icon? Does the app crash? What do you mean you cannot reinstall, what does it show in the store when you go to the app?
Often when you do the big upgrades your phone would take time to re-download and install all the apps, if you go the app list during that time you will see that they are sort of grayed out, and you have to wait for them to finish installing. If you tried to access the app during that time (around the first 30 min or so after your update, depending on how many apps you have), it won't open because it's not installed, the icons are just placeholders.