I'm having problems messaging people.
When I press enter on their name for example Johnson I get a message that they wish to receive messages from friends even though they're on my friends' list.

Hello,
it is possible that they have removed you. In this case, you will still be able to see them in your list, but they won't have you, and you won't of course be able to message them if they have their privacy configured as such.
Alternatively, there is another small bug with this, if someone changes their nickname, it is necessary for you to restart the Playroom for everything to work correctly.