While I haven't had the issue with Anthem itself I have had an issue in the past where a game has either frozen or overheated the system meaning I had to shut it down via removal of the power cable for the first or it wouldn't turn it back on for the second and the fix was exactly what the anthem devs have said. Boot it in safe mode which then lets it boot up normally so it wouldn't be the first time I've heard of the issue, although it being on such a large scale is certainly unusual.

I use a bog standard 1st gen PS4 if anyone cares.