Updating a game causes me to have to reinstall the ENTIRE THING

I would recommend moving all your games to the external storage and factory resetting the Xbox sadly this could be the only way to fix the issue because I don't believe power cycling the Xbox will fix this issue but if you would like to try doing that
hold down the power button for 10 seconds then when the system shut down unplug it from the wall for 2 minutes then plug it back in but I recommend what I said before in factory resetting the Xbox I know it's not the best answer but it should no matter what
fix the issue unless the games that are reinstalling instead of updating correctly are on the external then I would recommend first reformatting the external storage which should fix the problem hopefully this helps

What Games you try Update?

If the external hard drive is the possible cause then try and update something while the hard drive is disconnected.

It may be that your game is on the external hard drive but your default location for downloading games in your internal hard drive so when it goes to update it can't find the game as it isn't in the default location. If this is the case you would need to
make sure that the games being updated are on the internal hard drive before updating.

It happens quite often if there is an update that is already in progress and you cancel it, as if you uninstall the game and it is uninstalled, I do not know why it is. It has already happened to me once. Watch that.

Xbox only reinstalls the game during an upgrade if it is canceled.