I'm having the same issue too.
The update failed every time at 19.06GB. I uninstalled the game, try to reinstalling it (I own the physical Ultimate Edition) and it immediately stops installing giving me the vague message of something went wrong with an error code of 0x80070057. Yet it puts a 25.8GB file for Halo Wars 2 in my games list.
I uninstall that and it puts a 42 ish GB file in my ready to install list, which is the same file that stops installing at 19.06 GB, which happens again.
I uninstall that, try installing it from disc again, get the same vague message and error code, yet it puts the 25.8GB file for Halo Wars 2 in my games list. This also happens if I try installing it while not connected to the internet.
I uninstall that, it puts the 42 ish GB file in my ready to install list and the cycle continues.
Whenever I try to uninstall it and some how manage to get it to disappear from the ready to install section, I turn the console completely off, unplug it, leave it for a few minutes, plug it back in and turn it on. Once the console is back on the 25.8GB file is somehow magically back in the my games list, which gives me the same vague message and error code as before.
I uninstall that, it puts the 42 ish GB file in my ready to install list and the cycle continues yet again.
Seriously Devs, did you even test this update? I had no issues at all before this and now I can't play the game at all.
I refuse to factory reset the console for one game, especially since I have 97 other games installed and they all work without any issues at all. I shouldn't have to factory reset the console because an update you guys did completely broke the game, particularly since even doing that isn't working for some people either.
I was on call with Xbox support for an hour and nothing they suggested worked.
Please fix your game!