Epic Fail after V3 Installation migration

**Sonarr version **: 3.0.3.824

OS: Windows 10 Pro
Debug logs:
https://pastebin.com/raw/GUsCZH8v

https://pastebin.com/raw/hUBHRpxp

Description of issue:
Copied from Github bug report:
Installation has halted at the point of trying to remove the existing Sonarr V2 service (which was stopped)
However that appears to be a red herring based on the logfile attached

After manually copying in the config file and original db from my V2 backup - the migration appeared to proceed correctly (according to the debug logs) but no information on my existing library was imported, nor any of the settings.
It seemed to create a fresh, empty installation.