Navigate to the below folder
C:\Users\YOURUSERNAME\AppData\Local\Packages\Microsoft.FlightSimulator_8wekyb3d8bbwe\SystemAppData\wgs
Inside this folder are 2 folders, one called t, and the other has a long string of letters/numbers. Open this folder.
In this folder are several more folders. I went into each one of these folders and opened all of the files inside using notepad.
Most of them contain saved control mappings. Ignore those.
One of them contained lots of garbage text but also some file names of packages that are ‘ignored’ by the installer. Check the file to see if any of your missing packages are there. I made an edit to this file (Just added a random space in it) and saved it, which effectively corrupts the file.
This forces a new one to be generated which rectified the issue with packages not being downloaded. The installation manager is now able to pick up all mandatory content.
This has 100% fixed the issue for me. Let me know if you need any help navigating to or finding the file.