I think I found a fix.. Maybe...
Inspired by Princessbe_qrpr, and having tried and failed to install it and gone through all the various troubleshooting steps, I did the following:
- Cancelled the queued install that was stuck at 50% (this had been installed with disk 1 / disk 2, but hung)
- Not sure if it makes much of a difference but when it hung on disk 1, I had put disk 2 in to progress it, which it did, but then asked for disk 1 again and hung as normal.
- Went into manage game and uninstalled the game entirely as it was reporting it was installed even though it never finished
- Did not reboot, did not remove disk 1 from the xbox
- Clicked on the game tile of the disk as it was still in (disk 1) and it started installing and worked as normal
- Game then loaded, with disk 1 still in the drive
Hope this helps others...