From following some advice online of how to work around the Sons of Ragnar "talk to ubba" issue, I tried to play offline to see if I could get the game to move forward.
This resulted in every local save file I had showing as corrupt. My online saves still showed as available.
The next time I booted the game, back online and connected to PSN, I got the splash screen, then nothing, then my PS4 shut off. It has not worked properly since.
I have gone as far as to do a complete factory reset of the console and attempt to reinstall ACV, once copying from the blu-ray was complete I tried to launch and have now arrived at the exact same problem all over again.