2 step verification has not worked in a long time correctly on PS4 if you have had that onuring the life of facebook usage on PS4 it will stop the PS4 from connecting but as its now broken even more it will BLOCK new connections on the same account that had 2 step on...
Its all facebooks side and for facebook to fix NOTHING changed PS4, others are still linked fine..
This not firmware 6.20 issue its happened to users who were on 6.00, 6.10 and 6.20...
Not a new issue its just as Cookie links to server expire users are forced to relink to services so noncompliance of accounts shows up...
If facebook see a big enough dip in Advert viewing resulting in loss of money they will fix it if they don't they will ignore it..