Can't enable .NET Environment in Windows 10 1903

Hi Don (and thanks for all the info you shared here),

I did try a .NET installer, but it only said that .NET is already installed. 

But I did manage to solve this, without (clean) reinstalling and without the 20H1 insider build. I am not sure which step(s) solved it, but here is what I did (I will also include my initial steps that lead to the problem):

1. Join Release Preview ring, and update 1809 to 1903 build 18362.113. Everything worked here.
2. Few days later (yesterday) CU to 18362.116 came. Installed it, rebooted, and BOOM, .NET was gone.
3. Here I tried installing .NET using the Windows Features window, did not help. Also tried installing .NET from installer, it said .NET is already installed.
4. Reverted to previous build (1809), from where I started. .NET was still broken, although some things worked, but not everything, PowerShell and Visual Studio were broken.
5. I exited Windows Insider builds at this point.
6. I turned .NET off in Windows Features, rebooted, turned it back on again. This did not solve the problem, and I was still in a partially functional .NET situation (I think 3.5 worked and 4.x was broken).
7. I downloaded from MSDN an ISO with 1903, double clicked that (mounted to a drive), double clicked setup.exe and proceeded to do an in place upgrade, keeping apps and settings. I am on Windows 10 Pro, and I donwloaded an ISO for en_ culture, that was tagged (consumer versions).
8. This lasted a record long time, several hours, before it completed.
9. I ended up with 18362.30. But .NET was working again, and in fact now I had different entries in the Windows Features dialog than before (Don mentioned a working version and a non working version, I had the working one now).
10. Windows Update found a CU that brought me up to 18362.53. As I am no longer on the release preview branch, it does not find any more updates at the moment. .NET is still working.

So now I am on 1903, although a bit dated build, and no more builds are coming for the time being. .NET is working. But I feel this situation is a bit volatile, because I have no idea what fixed this for me, or what caused it in the first place. 

I tweeted this thread and the Feedback Hub issue to MS yesterday, plus asked my colleague who is a Regional Director if he could ping someone from MS with these information. Hopefully someone somewhere notices!

Curious that this problem seemed to have broken the previous Windows version as well, which is something I never encountered before. Usually reverting means I get my computer working again. 

I am suspecting that by opting to install from an ISO, it did not try to reuse things from my current install (to save bandwidth by not downloading everything) and instead installed everything from the ISO. But at this point this is just a theory.

Confirmed. I switch to the Fast track to get 18898.1000, and the .net framework is restored.

Unfortunately, this only worked on build 18362.86 (after the problem was first replicated on that same build, by using PowerShell to disable & remove all Optional Features).

I tried, on the same device, reverting to 18362.30 and doing this removal and repair again, but it did not work.  Also, I then upgraded (with .NET already gone) to 18362.86 and I cannot Enable .NET.

From what I have read, .NET issues have sometimes only been repairable if any subsequent KB update is first uninstalled. So once .NET has failed, or has been removed, and a new KB has been installed, you can't fix it.

The CBS and DISM logs indicate missing Parent Features, which prevent the remaining, listed .NET Features from being Enabled.

So far, I am happy to report that after installing KB4497093 (18362.86) I am no longer able to replicate the failed .NET situation.  I have attempted to entirely remove and replace .NET 3.5 and .NET 4.x and Windows was able to restore them via Windows Update. The Parent services displayed in optionalfeatures.exe did not vanish and create the unusual list of sub-features that have been shown in this thread.

I do not believe that this repairs .NET on a device that has this condition, but it does provide a potentially stable .NET, as long as you can get the workstation to 18362.86 with .NET intact (after a clean install).

Also, note that you can upgrade directly from 18362.30 to 18362.86 via Windows Update.  You should not see, nor require, the superseded KB4495666.

Well, that ends my participation in Windows Insider. I  will never install another Windows update unless it's been vetted and is -3. How does Microsoft defend a release like this that disables your computer? Is there NO quality control? Totally unacceptable.