Avast Free doesn't work after update

[REDACTED]

I had no trouble with v12 until last week when I updated to v17

The update process "completed" and prompted a restart. I restarted.
Slow start, log-in and... Avast failed to start.

I saw the icon flash and disappear. The UI starts, the tray icon gets added and disappears.

So, restart, repair, restart, repair... nothing
Uninstall, restart, install, restart.... it "kind of" works.

Main interface is blank. I can trigger part of the interface via the tray icon->About
And there half of the things work. Update does not. Register causes a blank window to appear (it disappears after a minute)

Any ideas, I'm up to another uninstall/install process, but I am a bit skeptical on that working after last clean installation.

I'm using Windows 10 Pro 64 bit, English Locale.
Installation path: q:\program files\avast

[Eddy]

Did you use avastclear ?

[REDACTED]

Yes, even though at first it didn't start in safe mode (missing file), but I restarted to normal mode and run it from there, which prompted me to restart in safe mode and it worked

After that I rebooted and checked manually for files at c:\ProgramData\avast, q:\program files\avast and c:\users\jmont\AppData\Avast and the registry for AVAST Registry Keys
I manually deleted the remaining files at c:\ProgramData\Avast, and run the offline installer (re-downloaded it today, just in case it was updated)

It failed to complete the install with an Access Violation error on AvastUI

[Eddy]

Have you tried to install in the default folder ?
Is Q: a removable drive ?

[REDACTED]

No, Q: is a HDD partition I use to install my applications.

I may try to install to the default C:\Program Files folder, but I'd rather not install applications there. It is a small disk reserved mainly for Windows.