'application://chromium_chromium.desktop' : this looks correct, the icon shouldn't disappear with every update. However I just managed to observe the problem in a xenial VM when refreshing the chromium snap from the stable to the beta channel. I'm suspecting Unity thinks the application is being uninstalled, so it removes the entry from the favorites, instead of just hiding it, like gnome-shell does.
'application: //chromium_ chromium. desktop' : this looks correct, the icon shouldn't disappear with every update. However I just managed to observe the problem in a xenial VM when refreshing the chromium snap from the stable to the beta channel. I'm suspecting Unity thinks the application is being uninstalled, so it removes the entry from the favorites, instead of just hiding it, like gnome-shell does.