Having the same message, only I was actually playing the game when the error occurred.

I was exiting a Raid but got stuck in the loading screen. Screen completely froze up (loading icon was not spinning). Ps4 was running fine in the background. Game froze, but system was fine. Waited, but nothing happened, so I was forced to restart the game. Closed the application and restarted, but instead of the log in screen I got an error message for error code NP-36147-1. I Can also hear the music in the background, but the log in screen will not display.

Side note. Ps4 connectivity seems fine. Been playing other games online and chatting with friends ever since. PSN is not under maintenance, and I have no pending updates. Seems like the problem is on SE's end of things.