You can't set up a chat party on your own for players to join. You have to set up a message chat group and select who you want to be in it. They are assuming that you play with the same group of people all the time.
I don't want to have to create a group for every combination of players who I have in chat - or then have to do the housework to tidy them up at some point.
I have notifications on for messages and this now goes off every time any one in a group I have been in starts a party chat.
Despite reports of firmware 9.0 bricking consoles, there's no official word, so may just be the regular small percentage having issues. (could be related to non-compatible HDDs).
In other news, it's meant to fix a battery/date issue: