I had the thing happen too..It all started off like a normal update - this was at 9:am local time yesterday.
The install was finally complete at 11
M last night.
The primary update installation was jank, with the loading bar going forward -stalling - then unwinding - then progressing again.
Then the content manager updates were jank - with the 'updates failed to install' messages - loading bars running forward and backward (looping) and on and on.
I cancelled all and closed MSFS the first attempt - restarted the PC -went to the Xbox site and checked for further app updates, and tried again - same sauce.
This time I just let it run - left the PC on and found other stuff to do. Eventually the main MSFS update dropped in and the sim opened so I could go to the content manager and try again to get the rest of the SU installed
Which one is this again ? 13!!? no wonder.
Anyway - I still had a number of 'failed to install' issues but updated the ones I could - then 'cancelled' the rest and closed MSFS - then restarted the PC and tried again.
This time I was able to get the remaining packages to install and then I ran a short flight just to make sure it was working - no CTD or other issues yet.
This is the first update since SU3 that gave me trouble. And I mean I checked internet connections and speed, reviewed all of my PC and antivirus settings, but when I checked the main forums it became obvious this wasn't an end user problem.