Once the game has loaded and you are in game playing, the "social" friends list will not update to reflect the true number of pS4 friends online.
I had 4 friends online when I began the game yesterday. I had 3 more hop on and ask for invites. I could not see them online but they could see me. I had to logout and log back in just to update my list.
So I’ve attached the following images showing who’s online in my friends list then also a video showing my Division Social doesn’t recognise they’re online so you can only invite
https://youtu.be/V01ahcC6OQ4
https://imgur.com/gallery/ESYSZ5d
Basically what our group noticed was that DIV2 took note of who was online at the point you start the game and that is who you will always see even if they log off or new people log in.
It just wasn't refereshing the current list.
For the join squad a workaround we used was to use the PS4 Join Game feature from the dashboard. That worked flawlessly the entire weekend.