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.

This is also happening to me, trying to interact with the PS4 is just causing it to switch off completely.