Notating the overall solution for anyone else with the issue in the future:
The ultimate solution was to completely remove DCS from the PC.
Backup your inputs etc first.
Reinstalled on a DIFFERENT drive to the OG installation location and it works fine.
Unfortunately I think in my case it was a hardware failure caused by a hardware situation, ie: the SATA cable was loose and not pushed all the way home so the SSD was not getting a great connection. Potential for bit flip was very high. I didn't catch it in time and I suspect that drive is cooked.
