I have a handful of existing friends in my list, however each time I start the game anyone added in the last session is no longer listed even when the game has been exited using the quit button so not due to a crash or the like.
Are you using the Uber-launcher or Steam Version? Or are you using PAMM with auto-login? There is a bug with the Uber-launcher version resetting the display name and that could apply to the PAMM start with login too. It could be related. See here, point 8: https://forums.uberent.com/threads/know-issues.65155/
more information, removing a friend has the same effect, upon restarting they're back in the list, it's as if the friends list is read only.
Could you post the Coherent_UI.log file from when that happens? It lives in the same directory as PA.exe.
Hmm, I was "hoping" to see a write error in there, but everything seems to be fine. I rarely use the friends feature, so I don't know if it's generally broken or just specifically for you... Do your friends suffer from the same problem?
Something weird is going on, I've now managed to add some new friends that are sticking though removing is inconsistent. I don't know if this a known issue but friends showing online randomly switch their order.