projects corrupted: Copying assembly.....UnityEngine.TestRunner.dll' failed

A few days ago I switched from editing a script in Visual Studio back to Unity (2019.2.10), using HDRP which crashed Unity - when I opened the project again, only a few items in my scene were visible at all, with pink error materials, most items were not visible in the scene and all references to any scripts showed missing script / not monobehaviour.

In the console, I have these two errors:

Copying assembly from 'Temp/UnityEngine.UI.dll' to 'Library/ScriptAssemblies/UnityEngine.UI.dll' failed

Copying assembly from 'Temp/UnityEngine.TestRunner.dll' to 'Library/ScriptAssemblies/UnityEngine.TestRunner.dll' failed

I tried reinstalling unity, installing a newer version (unity 2019.2.10 to 2019.2.11, also tried with latest Beta) and have same issue and errors with the project folder. I have a backup folder from a week ago, which when I open it on the same PC results in the same error - I also see that the \Library\ScriptAssemblies folder becomes empty after being opened in unity on this PC. I've tried copy pasting everything from that folder back in after opening, no change.

I opened the backup folder on a different PC with 2019.2.11 and was able to open it as normal - however the folder that appears to have been corrupted on the other PC results in the same issue on either PC.

It appears that opening any of my projects (pre-crash and post-crash) results in them being irretrievably corrupted on my main desktop - my other laptop can run a pre-crash project no problem, but that laptop is not good enough to run VR, so I can't use it for developing this project.

I've tried all of the fixes provided by other users here: Nothing works at all:

• I have already uninstalled and deleted both versions of Unity, looked for key in registry (found nothing), deleted everything in a unity folder in appdata folder

• tried reimporting all assets, resetting packages to default

• I have also tried disabling antivirus, scanning for viruses, (found a bit miner but still having same problem)

• ensuring I have full admin control of the folders in my project

• deleting temp folders

• starting a new project and importing a custom package that I exported which included most of the assets in my project, (scripts, scene, models, prefabs)- importing the asset package causes the same issue (on my desktop, not on my laptop.)

• opening visual studio and editing a script then going back to unity, no change.

• I'm not using collaborate or multiplayer package.

• The problem never goes away by restarting unity

• List item

My next option is to reinstall windows, but as I seem to have removed unity fully already I don't know will this definitely fix things - if anyone has any other solutions please help! I have filed a bug report also.